Method and apparatus for accessing a wireless network

ABSTRACT

Methods and apparatuses for accessing a wireless network are described herein. A method according to at least one embodiment may include receiving a transmission including information associated with a plurality of random access channel (RACH) configurations. The information may indicate a plurality of RACH occasions in which a preamble transmission may be sent. One or more reference signals may be received. Methods may further include sending, using one of the plurality of RACH configurations, the preamble transmission in one of the plurality of RACH occasions along with one or more protocol data units (PDUs). The one of the plurality of RACH configurations may be selected based on a measurement of at least one of the one or more received reference signals. The method may further include sending, in response to the preamble transmission and the one or more PDUs, a random access response.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of U.S. patent application Ser. No.16/818,093 filed on Mar. 13, 2020, which issued as U.S. Pat. No.11,284,445 on Mar. 22, 2022, which is a continuation of U.S. patentapplication Ser. No. 16/086,880, filed Sep. 20, 2018, which is the U.S.National Stage, under 35 U.S.C. § 371, of International Application No.PCT/US2017/024966, filed Mar. 30, 2017, which claims the benefit ofProvisional Application No. 62/315,458, filed Mar. 30, 2016, thecontents of which are incorporated herein by reference.

BACKGROUND

Mobile communications are in continuous evolution and are at thedoorstep of its fifth incarnation, 5G. As with previous generations, newuse cases largely contributed in setting the requirements for the newsystem. The 5G air interface may at least enable the following usecases: improved broadband performance (IBB); industrial control andcommunications (ICC) and vehicular applications (V2X); and massivemachine-type communications (mMTC).

The above uses cases may be translated into the following requirementsfor the 5G interface: support for ultra-low transmission latency (LLC);support for ultra-reliable transmission (URC); and support for MTCoperation (including narrowband operation).

One of the goals for the next generation radio access technology is toachieve improved energy efficiency. Energy consumption in the radioaccess network is dominated by always-on broadcast signaling.

SUMMARY

Methods and apparatuses for accessing a wireless network are describedherein. A method according to at least one embodiment may includereceiving a transmission including information associated with aplurality of random access channel (RACH) configurations. Theinformation may indicate a plurality of RACH occasions in which apreamble transmission may be sent. One or more reference signals may bereceived. Methods may further include sending, using one of theplurality of RACH configurations, the preamble transmission in one ofthe plurality of RACH occasions along with one or more protocol dataunits (PDUs). The one of the plurality of RACH configurations may beselected based on a measurement of at least one of the one or morereceived reference signals. The method may further include sending, inresponse to the preamble transmission and the one or more PDUs, a randomaccess response.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A;

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A;

FIG. 2 is a diagram that provides an example of some of the systemtransmission bandwidths supported by a 5gFLEX system;

FIG. 3 is a diagram of an example flexible spectrum allocation supportedby a 5gFLEX system;

FIG. 4 is a diagram of an example flexible frame structure for TDD thatmay be used in a wireless communications system such as a 5gFLEX system;

FIG. 5 is a diagram of an example frame structure for FDD that may beused in a wireless communications system such as a 5gFLEX system;

FIG. 6 is a diagram of the example assistance modes available;

FIG. 7 is a diagram of an example system for initial access using systemsignatures or signature sequences;

FIG. 8 is a flow diagram of an example process for initial access usingsystem signatures or signature sequences;

FIG. 9 is a flow diagram of an example process for detecting/acquiringsystem information via access tables;

FIG. 10 is a flow diagram of an example random access procedure usinginitial access using system signatures or signature sequences; and

FIG. 11 is a flow diagram of an example procedure for configuration ofdiverse access methods.

DETAILED DESCRIPTION

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications system 100may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN) 104, a core network 106, a public switchedtelephone network (PSTN) 108, the Internet 110, and other networks 112,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the other networks 112. By way of example, the base stations 114a, 114 b may be a base transceiver station (BTS), a Node-B, an eNodeB(eNB), a Home Node B, a Home eNodeB, a site controller, an access point(AP), a wireless router, and the like. While the base stations 114 a,114 b are each depicted as a single element, it will be appreciated thatthe base stations 114 a, 114 b may include any number of interconnectedbase stations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple-output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as Institute for Electricaland Electronics Engineers (IEEE) 802.16 (i.e., WorldwideInteroperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1×,CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95(IS-95), Interim Standard 856 (IS-856), Global System for Mobilecommunications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSMEDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNodeB, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks112 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers,transmitters, or receivers for communicating with different wirelessnetworks over different wireless links. For example, the WTRU 102 cshown in FIG. 1A may be configured to communicate with the base station114 a, which may employ a cellular-based radio technology, and with thebase station 114 b, which may employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and receive both RF and light signals. It will be appreciatedthat the transmit/receive element 122 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 and the removable memory 132 may includeany volatile or non-volatile read/write memory. The non-removable memory130 may include random-access memory (RAM), read-only memory (ROM), ahard disk, or any other type of memory storage device. The removablememory 132 may include but is not limited to a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown). The processor 118 may access information from, and store datain, an access table stored in any type of suitable memory, such as thenon-removable memory 130 and/or the removable memory 132. The accesstable that is stored in any type of suitable memory, such as thenon-removable memory 130 and/or the removable memory 132, may bereceived from communication networks, such as the core network 106, theInternet 110, and/or the other networks 112, or any of the 3GPP or 5Gnetwork entities described herein.

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 104 and the core network 106according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116. The RAN 104 may also be in communicationwith the core network 106.

The RAN 104 may include eNodeBs (eNBs) 140 a, 140 b, 140 c, though itwill be appreciated that the RAN 104 may include any number of eNodeBswhile remaining consistent with an embodiment. The eNodeBs 140 a, 140 b,140 c may each include one or more transceivers for communicating withthe WTRUs 102 a, 102 b, 102 c over the air interface 116. In oneembodiment, the eNodeBs 140 a, 140 b, 140 c may implement MIMOtechnology. Thus, the eNodeB 140 a, for example, may use multipleantennas to transmit wireless signals to, and receive wireless signalsfrom, the WTRU 102 a.

Each of the eNodeBs 140 a, 140 b, 140 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 1C, theeNodeBs 140 a, 140 b, 140 c may communicate with one another over an X2interface.

The core network 106 shown in FIG. 1C may include a mobility managemententity (MME) 142, a serving gateway 144, and a packet data network (PDN)gateway 146. While each of the foregoing elements are depicted as partof the core network 106, it will be appreciated that any one of theseelements may be owned and/or operated by an entity other than the corenetwork operator.

The MME 142 may be connected to each of the eNodeBs 140 a, 140 b, 140 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 142 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 142 may also provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM or WCDMA.

The serving gateway 144 may be connected to each of the eNodeBs 140 a,140 b, 140 c in the RAN 104 via the S1 interface. The serving gateway144 may generally route and forward user data packets to/from the WTRUs102 a, 102 b, 102 c. The serving gateway 144 may also perform otherfunctions, such as anchoring user planes during inter-eNodeB handovers,triggering paging when downlink data is available for the WTRUs 102 a,102 b, 102 c, managing and storing contexts of the WTRUs 102 a, 102 b,102 c, and the like.

The serving gateway 144 may also be connected to the PDN gateway 146,which may provide the WTRUs 102 a, 102 b, 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and IP-enableddevices.

The core network 106 may facilitate communications with variousnetworks. For example, the core network 106 may provide the WTRUs 102 a,102 b, 102 c with access to circuit-switched networks, such as the PSTN108, to facilitate communications between the WTRUs 102 a, 102 b, 102 cand traditional land-line communications devices. For example, the corenetwork 106 may include, or may communicate with, an IP gateway (e.g.,an IP multimedia subsystem (IMS) server) that serves as an interfacebetween the core network 106 and the PSTN 108. In addition, the corenetwork 106 may provide the WTRUs 102 a, 102 b, 102 c with access to thevarious networks including the PSTN 108, Internet 110, and othernetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

Other networks 112 may further be connected to an IEEE 802.11 basedwireless local area network (WLAN) 160. The WLAN 160 may include anaccess router 165. The access router may contain gateway functionality.The access router 165 may be in communication with a plurality of accesspoints (APs) 170 a, 170 b. The communication between access router 165and APs 170 a, 170 b may be via wired Ethernet (IEEE 802.3 standards),or any type of wireless communication protocol. AP 170 a is in wirelesscommunication over an air interface with WTRU 102 d.

Although the embodiments described herein consider 3GPP specificprotocols, the embodiments described herein are not restricted to a 3GPPsystem and are applicable to other wireless systems.

While not intending to limit the applicability to other meanings and/orother type of signals, configuration methods, or logical associationsbetween different user data units, the following definitions and termsare used herein in support for the description of the various methods.

The following abbreviations and acronyms are provided to aid and enhancethe understanding of the embodiments described herein.

-   -   Δf Sub-carrier spacing    -   5gFlex 5G Flexible Radio Access Technology    -   5gNB 5GFlex NodeB    -   ACK Acknowledgement    -   BLER Block Error Rate    -   BTI Basic TI (in integer multiple of one or more symbol        duration)    -   CB Contention-Based (e.g., access, channel, resource)    -   CoMP Coordinated Multi-Point transmission/reception    -   CP Cyclic Prefix    -   CP-OFDM Conventional OFDM (relying on cyclic prefix)    -   CQI Channel Quality Indicator    -   CN Core Network (e.g., LTE packet core)    -   CRC Cyclic Redundancy Check    -   CSG Closed Subscriber Group    -   CSI Channel State Information    -   D2D Device to Device transmissions (e.g., LTE Sidelink)    -   DCI Downlink Control Information    -   DL Downlink    -   DM-RS Demodulation Reference Signal    -   DRB Data Radio Bearer    -   EPC Evolved Packet Core    -   FBMC Filtered Band Multi-Carrier    -   FBMC/OQAM A FBMC technique using Offset Quadrature Amplitude        Modulation    -   FDD Frequency Division Duplexing    -   FDM Frequency Division Multiplexing    -   ICC Industrial Control and Communications    -   ICIC Inter-Cell Interference Cancellation    -   IP Internet Protocol    -   LAA License Assisted Access    -   LBT Listen-Before-Talk    -   LCH Logical Channel    -   LCP Logical Channel Prioritization    -   LLC Low Latency Communications    -   LTE Long Term Evolution e.g., from 3GPP LTE R8 and up    -   MAC Medium Access Control    -   NACK Negative ACK    -   MC MultiCarrier    -   MCS Modulation and Coding Scheme    -   MIMO Multiple Input Multiple Output    -   MTC Machine-Type Communications    -   NAS Non-Access Stratum    -   OFDM Orthogonal Frequency-Division Multiplexing    -   OOB Out-Of-Band (emissions)    -   Pcmax Total available WTRU power in a given TI    -   PHY Physical Layer    -   PRACH Physical Random Access Channel    -   PDU Protocol Data Unit    -   PER Packet Error Rate    -   PLMN Public Land Mobile Network    -   PLR Packet Loss Rate    -   PSS Primary Synchronization Signal    -   QoS Quality of Service (from the physical layer perspective)    -   RAB Radio Access Bearer    -   RACH Random Access Channel (or procedure)    -   RAR Random Access Response    -   RCU Radio access network Central Unit    -   RF Radio Front end    -   RNTI Radio Network Identifier    -   RRC Radio Resource Control    -   RRM Radio Resource Management    -   RS Reference Signal    -   RTT Round-Trip Time    -   SCMA Single Carrier Multiple Access    -   SDU Service Data Unit    -   SOM Spectrum Operation Mode    -   SS Synchronization Signal    -   SSS Secondary Synchronization Signal    -   SRB Signaling Radio Bearer    -   SWG Switching Gap (in a self-contained subframe)    -   TB Transport Block    -   TBS Transport Block Size    -   TDD Time-Division Duplexing    -   TDM Time-Division Multiplexing    -   TI Time Interval (in integer multiple of one or more BTI)    -   TTI Transmission Time Interval (in integer multiple of one or        more TI)    -   TRP Transmission/Reception Point    -   TRPG Transmission/Reception Point Group    -   TRx Transceiver    -   UFMC Universal Filtered MultiCarrier    -   UF-OFDM Universal Filtered OFDM    -   UL Uplink    -   URC Ultra-Reliable Communications    -   URLLC Ultra-Reliable and Low Latency Communications    -   V2V Vehicle to vehicle communications    -   V2X Vehicular communications    -   WLAN Wireless Local Area Networks and related technologies (IEEE        802.xx domain)

One of the goals for next generation radio access technology such as5gFLEX is to achieve improved energy efficiency. Energy consumption inthe radio access network may be due to always-on broadcast signaling.Reducing mandatory periodic transmissions that are not directly relatedto user data transmission is one solution provided by the embodimentsdescribed herein.

Next generation radio access technology such as 5gFLEX is also expectedto support diverse sets of services in the same spectrum. Legacy LTEsystems may define one initial access method for example, random access,but in 5G diverse sets of access methods may be used to handle differentuse cases including but not limited to enhanced mobile broadband (eMBB),mMTC, and URLLC. Mechanisms to handle a diverse set of access methods isanother solution provided by the embodiments described herein.

The embodiments described herein may be used in deployment scenariosincluding but not limited to (1) LTE-assisted 5gFLEX Aggregation(DC/CA/Offload), (2) LTE-assisted 5gFLEX Transport Channel(s) (whichincludes for example, LTE CP, LTE UP, LTE Uu with one or more 5gFLEXTrCH/Physical channels plugged into LTE Uu), LTE-based Stand-alone5gFLEX operation (which includes for example, LTE CP, LTE L2 at least inpart, 5gFLEX PHY), and (3) Stand-alone 5gFLEX operation.

For LTE-assisted 5gFLEX Aggregation (DC/CA/Offload), the WTRU may beconfigured using the LTE Control Plane, for example with a LTE RRCconnection, and using the LTE User Plane, for example with one or moreLTE Uu interfaces. The WTRU may further be configured to operate withone or more additional 5gFLEX Uu(s) using the principles of LTE DC, LTECA or LTE-WLAN offload. This configuration may be performed by receptionof access table(s) from broadcast or dedicated signaling. Triggers forinitial access to 5gFLEX PHY may use similar triggers as for LTECA/DC/Offload or other types of triggers.

For LTE-assisted 5gFLEX Transport Channel(s) (which includes forexample, LTE CP, LTE UP, LTE Uu with one or more 5gFLEX TrCH/Physicalchannels plugged into LTE Uu), the WTRU may be configured for LTE Uuoperation using legacy methods. The WTRU may be further configured withone or more physical layer (control and/or data) channels for a 5gFLEXUu of the configuration of the WTRU. The downlink physical channels mayco-exist in the DL carrier and/or frequency band while the UL carriermay also be common or separate (e.g., for uplink control channels). Fromthe perspective of the WTRU configured with one or more 5gFLEX physicalchannels, the cell-specific LTE signals/channels may be viewed as holesin the 5gFLEX map of physical layer resources. Triggers for initialaccess to 5gFLEX PHY may use similar triggers as for LTE DL data arrivaland/or LTE UL data arrival or other triggers as 5Gtransmission/reception points (TRPs) may not necessarily be collocatedwith the LTE eNB (e.g., 5G RRHs).

For LTE-based Stand-alone 5gFLEX operation (which includes for example,LTE CP, LTE L2, 5gFLEX PHY), the WTRU may be configured with componentsof the LTE control plane (for example, RRC connection, security, etc.)and with components of the LTE user plane (for example, EPS RABs, PDCP,RLC). The WTRU may also be configured with one or more 5G MACinstance(s) each with one or more 5gFLEX Uu(s). Triggers for initialaccess may be similar to the ones of a stand-alone 5gFLEX system or be avariation a stand-alone 5gFLEX system.

For stand-alone 5gFLEX operation, the WTRU may be configured with a 5Gcontrol plane and a 5G user plane. 5gFLEX Uu operation may be addressedin this case.

The methods and processes described herein may be performed on any ofthe devices described herein. In particular, the methods for initialaccess using system signatures or signature sequences may be performedon a WTRU, base station, AP, eNB, 5gNB, any other device describedherein, or any other device that is capable of operating in a wirelesscommunications system.

A system and method for providing access to a wireless communicationsystem, such as a 5gFLEX system, is described herein. The system andmethod may include receiving by a communications device a systemsignature or signature sequence, determining, via the received systemsignature or signature sequence, one or more parameters associated withthe wireless communication system, and accessing the wirelesscommunication system using the communications device based on the one ormore parameters. The embodiments described herein may be described usingvarious wireless technologies including the 5G air interface, 5gFLEX.However, such descriptions are for exemplary purposes and do not limitthe applicability of the embodiments described herein to other wirelesstechnologies and/or to wireless technology using different principles.

The embodiments described herein may be used in support of the use casesenabled by the 5G air interface including but not limited to IBB, ICC,V2X, and mMTC. Support for ultra-low transmission latency (LLC) mayinclude air interface latency as low as 1 ms RTT, which may support TTIsbetween 100 us and 250 us. Support for ultra-low access latency (forexample, time from initial system access until the completion of thetransmission of the first user plane data unit) may also be supported.At least ICC and V2X require end-to-end (e2e) latency of less than 10ms.

Support for ultra-reliable transmission (URC) may include transmissionreliability that is higher than legacy LTE systems. The transmissionreliability target for URC is 99.999% transmission success and serviceavailability. Mobility for speed in the range of 0-500 km/h may also besupported. At least IC and V2X require Packet Loss Ratio of less than10e-6.

MTC operation (including narrowband operation) may also be supported.The air interface may efficiently support narrowband operation (forexample, using less than 200 KHz), extended battery life (for example,up to 15 years of autonomy), and minimal communication overhead forsmall and infrequent data transmissions (for example, low data rate inthe range of 1-100 kbps with access latency of seconds to hours).

OFDM is used as the basic signal format for data transmissions in LTEand IEEE 802.11. OFDM efficiently divides the spectrum into multipleparallel orthogonal subbands. Each subcarrier is shaped using arectangular window in the time domain leading to sinc-shaped subcarriersin the frequency domain. OFDMA uses frequency synchronization and tightmanagement of uplink timing alignment within the duration of the cyclicprefix to maintain orthogonality between signals and to minimizeintercarrier interference. Such tight synchronization may also not bewell-suited in a system where a WTRU is connected to multiple accesspoints simultaneously. Additional power reduction is also typicallyapplied to uplink transmissions to be compliant with spectral emissionrequirements to adjacent bands, in particular in the presence ofaggregation of fragmented spectrum for the WTRU's transmissions.

Some of the shortcomings of conventional OFDM (CP-OFDM) may be addressedby more stringent RF requirements for implementations, especially whenoperating using a large amount of contiguous spectrum not requiringaggregation. A CP-based OFDM transmission scheme may also lead to adownlink physical layer for 5G that is similar to that of legacy systemwith, for example, modifications to pilot signal density and location.

Therefore, the 5gFLEX design may focus on other waveform candidatesalthough conventional OFDM remains a candidate for 5G systems at leastfor the downlink transmission scheme. Flexible radio access for 5G maybuild upon technologies such as OFDMA and legacy LTE systems.

The 5gFLEX downlink transmission scheme may be based on a multicarrier(MC) waveform characterized by high spectral containment (i.e. lowerside lobes and lower OOB emissions). Multicarrier modulation waveformsdivide the channel into subchannels and modulate data symbols onsubcarriers in these subchannels. MC waveform candidates for 5G includebut are not limited to OFDM-OQAM and UFMC (UF-OFDM).

With OFDM-OQAM, a filter is applied in the time domain per subcarrier tothe OFDM signal to reduce OOB. OFDM-OQAM causes very low interference toadjacent bands, does not need large guard bands, and does not require acyclic prefix. OFDM-OQAM may be the most popular FBMC technique.However, it is sensitive to multipath effects and to high delay spreadin terms of orthogonality thereby complicating equalization and channelestimation.

With UFMC (UF-OFDM), a filter is also applied in the time domain to theOFDM signal to reduce OOB. However, filtering is applied per subband touse spectrum fragments thereby reducing complexity and making UF-OFDMmore practical to implement. However, if there are unused spectrumfragments in the band, OOB emissions in these fragments may remain ashigh as for conventional OFDM. In other words, UF-OFDM may improve overOFDM at the edges of the filtered spectrum and not in the spectral hole.

The waveforms described herein are used for exemplary purposes.Accordingly, the embodiments described herein are not limited to theabove waveforms and may be applicable to other waveforms.

These waveforms may enable multiplexing signals with non-orthogonalcharacteristics (such as different subcarrier spacing) in frequency andthe co-existence of asynchronous signals without requiring complexinterference cancellation receivers and may facilitate the aggregationof fragmented pieces of spectrum in the baseband processing as a lowercost alternative to its implementation as part of the RF processing.

Co-existence of different waveforms within the same band may be used,for example, to support mMTC narrowband operation using SCMA. Anotherexample is supporting within the same band a combination of differentwaveforms, such as for example, CP-OFDM, OFDM-OQAM and UF-OFDM for allaspects and for both downlink and uplink transmissions. Suchco-existence may include transmissions using different types ofwaveforms between different WTRUs or transmissions from the same WTRU,which may be either simultaneously with some overlap or consecutive inthe time domain.

Further co-existence aspects may include support for hybrid types ofwaveforms, including but not limited to the following: waveforms and/ortransmissions that support at least one of a possibly varying CPduration (for example, from one transmission to another), a combinationof a CP and a low power tail (for example, a zero tail), a form ofhybrid guard interval using a low power CP and an adaptive low powertail, and the like. Such waveforms may support dynamic variation and/orcontrol of further aspects such as how to apply filtering (for example,whether filtering is applied at the edge of the spectrum used forreception of any transmission(s) for a given carrier frequency, at theedge of a spectrum used for reception of a transmission associated witha specific spectrum operation mode (SOM), per subband, or per groupthereof).

The uplink transmission scheme may use the same or a different waveformas used for downlink transmissions.

Multiplexing of transmissions to and from different WTRUs in the samecell may be based on FDMA and TDMA.

The 5gFLEX radio access design may be characterized by a very highdegree of spectrum flexibility that may enable deployment in differentfrequency bands with different characteristics. These characteristicsmay include different duplex arrangements, and different and/or variablesizes of the available spectrum including contiguous and non-contiguousspectrum allocations in the same or different bands. The 5gFLEX radioaccess design may support variable timing aspects including support formultiple TTI lengths and support for asynchronous transmissions.

Both TDD and FDD duplexing schemes may be supported in the embodimentsdescribed herein. For FDD operation, supplemental downlink operation issupported using spectrum aggregation. FDD operation supports bothfull-duplex FDD and half-duplex FDD operation. For TDD operation, theDL/UL allocation is dynamic; i.e. the DL/UL allocation may not be basedon a fixed DL/UL frame configuration. Rather, the length of a DL or a ULtransmission interval is set per transmission opportunity.

The 5G air interface design may enable different transmission bandwidthson both the uplink and the downlink ranging from anything between anominal system bandwidth up to a maximum value corresponding to thesystem bandwidth.

FIG. 2 is a diagram that provides an example of some of the systemtransmission bandwidths 200 supported by a 5gFLEX system that supportsmethods for initial access using system signatures or signaturesequences in accordance with any of the embodiments described herein.For single carrier operation, supported system bandwidths may include atleast 5, 10, 20, 40 and 80 MHz. In some embodiments, supported systembandwidths may include any bandwidth in a given range (for example, froma few MHz up to 160 MHz). Nominal bandwidths may have one or more fixedpossible values. Narrowband transmissions of up to 200 KHz may besupported within the operating bandwidth for MTC devices. It is notedthat system bandwidth 201, as used herein, may refer to the largestportion of spectrum that may be managed by the network for a givencarrier. For such a carrier, the portion of spectrum that a WTRUminimally supports for cell acquisition, measurements, and initialaccess to the network may be referred to herein as the nominal systembandwidth 202.

A WTRU may be configured with channel bandwidths 203, 204, and/or 205that are within the range of the entire system bandwidth. The configuredchannel bandwidths 203, 204, and 205 of a WTRU may or may not includethe nominal system bandwidth 202 part of the system bandwidth 201.Bandwidth flexibility may be achieved by the 5G air interface of FIG. 2because all applicable sets of RF requirements for a given maximumoperating bandwidth in a band may be met without the introduction ofadditional allowed channel bandwidths for that operating bandwidth dueto the efficient support of baseband filtering of the frequency domainwaveform. Methods to configure, reconfigure and/or dynamically changethe configured channel bandwidths 203, 204, and 205 of a WTRU for singlecarrier operation may be supported by the 5G air interface of FIG. 2 aswell as methods to allocate spectrum for narrowband transmissions withinthe nominal system bandwidth 202, system bandwidth 201, or configuredchannel bandwidths 203, 204, and 205.

The physical layer of a 5G air interface may also be band-agnostic andmay support operation in licensed bands below 5 GHz as well as operationin the unlicensed bands in the range 5-6 GHz. For operation in theunlicensed bands, LBT Cat 4 based channel access framework similar toLTE LAA may be supported. Methods to scale and manage (e.g., scheduling,addressing of resources, broadcasted signals, measurements)cell-specific and/or WTRU-specific channel bandwidths for arbitraryspectrum block sizes may also be supported.

Downlink control channels and signals may support FDM operation. A WTRUmay acquire a downlink carrier by receiving transmissions using only thenominal part of the system bandwidth; i.e. the WTRU may not initially berequired to receive transmissions covering the entire bandwidth that isbeing managed by the network for the concerned carrier.

Downlink data channels may be allocated over a bandwidth that may or maynot correspond to the nominal system bandwidth, without restrictionsother than being within the WTRU's configured channel bandwidth. Forexample, the network may operate a carrier with a 12 MHz systembandwidth using a 5 MHz nominal bandwidth allowing devices supporting atmost 5 MHz maximum RF bandwidth to acquire and access the system whilepossibly allocating +10 to −10 MHz of the carrier frequency to otherWTRU's supporting up to 20 MHz worth of channel bandwidth.

FIG. 3 is a diagram of an example flexible spectrum allocation 300supported by a 5gFLEX system that supports methods for initial accessusing system signatures or signature sequences in accordance with any ofthe embodiments described herein. The system bandwidth 301 may supportspectrum allocation with variable transmission characteristics 302 andthe nominal system bandwidth 303. In the example of FIG. 3 , thedifferent subcarriers 304 may be at least conceptually assigned todifferent modes of operation (e.g., SOM). Different SOM may be used tofulfill different requirements for different transmissions. A SOM mayinclude a subcarrier spacing, a TTI length, and/or one or morereliability aspects (e.g., hybrid automatic repeat request (HARQ)processing aspects) and possibly also a secondary control channel. SOMmay refer to a specific waveform or to a processing aspect (e.g.,support for co-existence of different waveforms in the same carrierusing FDM and/or TDM, or support for coexistence of FDD operation in aTDD band in a TDM manner or otherwise).

A WTRU may be configured to perform transmissions according to one ormore SOMs. For example, a SOM may correspond to transmissions that useat least one of the following: a specific TTI duration, a specificinitial power level, a specific HARQ processing type, a specific upperbound for successful HARQ reception/transmission, a specifictransmission mode, a specific physical channel (uplink or downlink), aspecific waveform type, or a transmission according to a specific RAT(for example, legacy LTE or according to a 5G transmission method). ASOM may also correspond to a QoS level and/or a related aspect, forexample, maximum/target latency, maximum/target BLER, or another QoSlevel or related aspect. A SOM may further correspond to a spectrum areaand/or to a specific control channel or aspect thereof (including searchspace, DCI type, etc.). For example, a WTRU may be configured with a SOMfor each of a URC type of service, a LLC type of service, and a MBB typeof service. A WTRU may have a configuration for a SOM for system accessand also for transmission/reception of L3 control signaling (forexample, RRC signaling) in a portion of a spectrum associated with thesystem such as in nominal system bandwidth 303.

Spectrum aggregation may be supported for single carrier operation,whereby the WTRU supports transmission and reception of multipletransport blocks (TBs) over contiguous or non-contiguous sets ofphysical resource blocks (PRBs) within the same operating band. A singleTB may also be mapped to separate sets of PRBs.

Simultaneous transmissions may be associated with different SOMrequirements. Multicarrier operation may also be supported usingcontiguous or non-contiguous spectrum blocks within the same operatingband, or across two or more operating bands. Aggregation of spectrumblocks using different modes (for example, FDD and TDD) and usingdifferent channel access methods (for example, licensed and unlicensedband operation below 6 GHz) may also be supported. The multicarrieraggregation of a WTRU may be configured, reconfigured, or dynamicallychanged.

Downlink and uplink transmissions may be organized into radio framescharacterized by a number of fixed aspects (for example, location ofdownlink control information (DCI)) and a number of varying aspects (forexample, transmission timing and supported types of transmissions).

A basic time interval (BTI) is expressed in terms of an integer numberof one or more symbol(s), where symbol duration may be a function of thesubcarrier spacing applicable to the time-frequency resource. For FDD,subcarrier spacing may thus differ between the uplink carrier frequencyf_(UL) and the downlink carrier frequency f_(DL) for a given frame.

A transmission time interval (TTI) may be the minimum time supported bythe system between consecutive transmissions where each would beassociated with different TBs for the downlink (TTI_(DL)), for theuplink (UL TRx) excluding any preamble (if applicable) but including anycontrol information (for example, downlink control information (DCI) oruplink control information (UCI)). A TTI may be expressed in terms ofinteger number of one of more BTI(s). A BTI may be specific and/orassociated with a given SOM.

Supported frame durations may include but are not limited to 100 us, 125us (1/8 ms), 142.85 us (1/7 ms is 2 nCP LTE OFDM symbols), and 1 ms toenable alignment with the legacy LTE timing structure.

FIG. 4 is a diagram of an example flexible frame structure 400 for TDDthat may be used in a wireless communications system such as a 5gFLEXsystem supporting initial access using system signatures or signaturesequences in accordance with one embodiment, which may be used incombination with any of the embodiments described herein. As shown inthe example of FIG. 4 , the start of each frame may be indicated by adownlink control information (DCI) 401 a and 401 b of a fixed timeduration t_(dci) 412 a and 412 b preceding any DL transmission portionof each frame (DL TRx) 402 a and 402 b for the concerned carrierfrequency, f_(UL+DL). The duration of the DL transmission portions 402 aand 402 b may be based on an integer number of transmit blocks (TBs).

In the example of FIG. 4 , the DCI 401 a may indicate at least durationt_(DL(n)) 405 a for the DL TRx portion 402 a for frame n, and DCI 401 bmay indicate at least duration t_(DL(n+1)) 405 b for the DL TRx portion402 b for frame n+1, in addition to any downlink assignment(s) and/orany uplink grant(s) indicated by the DCIs 401 a and 401 b.

The frame may also include an UL transmission portion of the frame (ULTRx) 403 a and 403 b. The duration of the UL transmission portions 403 aand 403 b may be based on an integer number of transmit blocks (TBs). Inthe example of FIG. 4 , the DCI 401 a may indicate at least durationt_(UL(n)) 406 a for the UL TRx portion 403 a for frame n, and DCI 401 bmay indicate at least duration t_(UL(n+1)) 406 b for the UL TRx portion403 b for frame n+1. If the uplink portion of the frame is present asshown in the example of FIG. 4 , a switching gap (SWG) 404 a and 404 bmay precede the uplink portion of each frame.

The WTRU may then derive the resulting TTI duration for each frame basedon the DCIs 401 a and 401 b. As shown in the example of FIG. 4 , thevariable duration of each frame may be expressed in terms of a TTIduration expressed in terms of an integer number of BTIs. In the exampleof FIG. 4 , the duration of frame n is expressed in terms of a TTI_(n)expressed as x*BTI 409 a, and the duration of frame n+1 is expressed interms of a TTI_(n+1) expressed as y*BTI 409 b. The example of FIG. 4also shows the inter-subframe spacing (ISS) 411.

For TDD, 5gFLEX may support device-to-device (D2D)/vehicle-to-everything(V2X)/Sidelink operation in the frame structure 400 by includingrespective downlink control and forward direction transmissions in theDCI and DL TRx portion (if a semi-static allocation of the respectiveresources is used). Alternatively, D2D/V2X/Sidelink operation may besupported in the frame structure 400 by including respective downlinkcontrol and forward direction transmissions in the DL TRx portion (fordynamic allocation) and by including the respective reverse directiontransmission in the UL TRx portion of the frame structure 400.

FIG. 5 is a diagram of an example frame structure 500 for FDD that maybe used in a wireless communications system such as a 5gFLEX systemsupporting initial access using system signatures or signature sequencesin accordance with another embodiment, which may be used in combinationwith any of the embodiments described herein. The frame structure 500may include a downlink reference TTI and one or more TTI(s) for theuplink. As shown in the example of FIG. 5 , the start of the frame maybe indicated by a DCI 501 a and 501 b of a fixed time duration t_(dci)506 a and 506 b preceding any downlink data transmission portion (DLTRx) 502 a and 502 b for the concerned carrier frequency f_(DL). Theduration of the DL transmission portions 502 a and 502 b may be based onan integer number of transmit blocks (TBs).

In the example of FIG. 5 , the DCI 501 a may indicate the durationt_(DL(n)) 507 a for the DL TRx portion 502 a for frame n, and DCI 501 bmay indicate the duration for t_(DL(n+1)) 507 b for the DL TRx portion502 b for frame n+1. As shown in the example of FIG. 5 , the variableduration of each frame may be expressed in terms of the downlinkreference TTI durations expressed in terms of an integer number of BTIs.In the example of FIG. 5 , the duration of frame n is expressed in termsof a TTI_(DL(n)) expressed as x*BTI 509 a, and the duration of frame n+1is expressed in terms of a TTI_(DL(n+1)) expressed as y*BTI 509 b.

The DCI(s) may indicate an offset (t_(offset)) 505 and the TTI durationfor any applicable uplink transmission(s) that contains a transportblock. Separate DCIs may also be used for the downlink and uplinkdirections. In the example, of FIG. 5 , the frame may include an uplinktransmission portion (UL TRx) 503 a, 503 b, and 503 c for the concernedcarrier frequency f_(UL). The duration of the UL transmission portions503 a, 503 b, and 503 c may be based on an integer number of transmitblocks (TBs). The start of an uplink TTI may be derived using the offset(t_(offset)) 505 applied from the start of the downlink reference framethat overlaps with the start of the uplink frame. The t_(offset) 505 mayinclude a timing advance, for example, in cases where UL synchronizationis applicable. In the example of FIG. 5 , DCI 501 a may indicate atleast duration t_(UL(n,0)) 508 a and t_(UL(n,1)) 508 b for the UL TRxportions 503 a and 503 b for frame n. DCI 501 b may indicate at leastduration t_(UL(n+1,0)) 508 c for the UL TRx portion 503 c for frame n+1.The example of FIG. 5 also shows the ISS 504.

For FDD, 5gFLEX may support D2D/V2x/Sidelink operation in the UL TRxportion of the frame structure 500 by including respective downlinkcontrol, forward direction, and reverse direction transmissions in theUL TRx portion (dynamic allocation of the respective resources may beused).

A scheduling function may be supported in the medium access control(MAC) layer. Scheduling modes including but not limited to the followingmay be used: (1) network-based scheduling for tight scheduling in termsof resources, timing, and transmission parameters of downlinktransmissions and/or uplink transmissions; and (2) WTRU-based schedulingfor more flexibility in terms of timing and transmission parameters. Forthese modes, scheduling information may be valid for a single or formultiple TTIs.

Network-based scheduling enables the network to tightly manage theavailable radio resources assigned to different WTRUs such as tooptimize the sharing of such resources. Dynamic scheduling is supportedin this mode.

WTRU-based scheduling enables the WTRU to opportunistically accessuplink resources with minimal latency on an as-needed basis within a setof shared or dedicated uplink resources assigned (dynamically or not) bythe network. Both synchronized and unsynchronized opportunistictransmissions are supported. Both contention-based transmissions andcontention-free transmissions are supported. Support for opportunistictransmissions (scheduled or unscheduled) may meet the ultra-low latencyrequirements for 5G and the power saving requirement of the mMTC usecase.

5gFLEX may support an association between data available fortransmission and available resources for uplink transmissions.Multiplexing of data with different QoS requirements within the same TBmay be supported as long as such multiplexing neither introducesnegative impact to the service with the most stringent QoS requirementnor introduces unnecessary waste of system resources.

A transmission may be encoded using a number of different encodingmethods, which may have different characteristics. For example, anencoding method may generate a sequence of information units. Eachinformation unit, or block, may be self-contained. For example, an errorin the transmission of a first block may not impair the ability of thereceiver to successfully decode a second block, and in particular if thesecond block is error-free and/or if sufficient redundancy may be foundin the second block or in a different block for which at least a portionwas successfully decoded. Examples of encoding methods also includeraptor/fountain codes whereby a transmission may consist of a sequenceof N raptor codes. One or more such codes may be mapped to one or moretransmission “symbols” in time. A “symbol” may thus correspond to one ormore sets of information bits, for example, one or more octets. Suchencoding may be used to add forward error correction (FEC) to atransmission whereby the transmission may use N+1 or N+2 raptor codes(or symbols, assuming a one raptor code symbol relationship) so that thetransmission may be more resilient to the loss of one “symbol,” forexample, due to interference or puncturing by another transmissionoverlapping in time.

Logical Transport Connectivity may be different than the logical channel(LCH) used for legacy LTE. An LCH may represent a logical associationbetween data packets and/or PDUs. Such an association may be based onsuch data units being associated with the same bearer (similar tolegacy) and/or being associated with the same SOM and/or slice. Forexample, the association may be characterized by at least one of achaining of processing functions, an applicable physical data (and/orcontrol) channel (or instance thereof), an instantiation of a protocolstack including a specific portion being centralized (for example, PDCPonly or anything except RF), and/or another portion closer to the edge(for example, MAC/PHY in the TRP or RF only) that may be separated by afronthauling interface. Different access procedures may be triggered asa function of the type of LCH for which data is available when thetrigger is based on data arrival.

Logical Channels Grouping (LCG) may be different than the LCH groupingor characterization used for legacy LTE. An LCG may consist of a groupof LCH using one or more criteria. The criteria may be that the one ormore LCH may have a similar priority level applicable to all LCHs of theLCG (similar to legacy). The criteria may also be that the one or moreLCH may be associated with the same SOM or type thereof or the sameslice or type thereof. This association may characterized by at leastone of a chaining of processing functions, an applicable physical data(and/or control) channel (or instance thereof), an instantiation of aprotocol stack including a specific portion being centralized (forexample, PDCP only, or anything except RF) and/or another portion closerto the edge (for example, MAC/PHY in the TRP or RF only) that may beseparated by a fronthauling interface.

A RAN slice may include the RAN functions, transport network functions,and resources (for example, radio resources and backhaul/fronthaulresources along with core network functions/resources required toprovide end-to-end services to the user). The terms RAN slice or slicemay be used interchangeably herein. The transport or core networkfunctions may be virtualized on a general purpose processor, run asnetwork functions on specialized hardware, or split between specializedhardware and general purpose hardware. A PLMN may comprise one or moreslices, wherein each slice is equivalent to a single, common, or generalpurpose network of an operator. Each slice may include one or more SOMsoptimized to support various services that the slice offers. Forexample, WTRUs served within a slice may have one or more of thefollowing aspects in common: services and/or QoE requirements (e.g.,ULLRC, eMBB, MMTC), WTRU categories (for example, CAT 0 to M and beyond,and additional categories may be defined for >6 GHz to differentiatebeamforming capability), coverage requirements (for example, normalcoverage, enhanced coverage), PLMN/operators, support of a specific Uuinterface (for example, LTE, LTE-Evo, 5G below 6 GHz, 5G above 6 GHz,Unlicensed), and served by same core network slice.

A Transport Channel (TrCH) as referred to herein may include a specificset of processing steps and/or a specific set of functions applied tothe data that may affect one or more transmission characteristics overthe radio interface. Legacy LTE defines multiple types of TrCHs,including, for example, the Broadcast Channel (BCH), the Paging Channel(PCH), the Downlink Shared Channel (DL-SCH), the Multicast Channel(MCH), the Uplink Shared Channel (UL-SCH), and the Random Access Channel(that typically does not carry any user plane data). The main transportchannels for carrying user plane data are the DL-SCH and the UL-SCH, forthe downlink and for the uplink, respectively.

For 5G systems, the augmented set of requirements supported by the airinterface may lead to the support of multiple transport channels, suchas for user and/or control plane data and for a single WTRU.Accordingly, the term TrCH as used herein may have a broader meaningthan when the term is used in reference to LTE systems. For example, atransport channel for URLLC such as the URLLCH, a transport channel formobile broadband (MBBCH), and/or a transport channel for machine typecommunications (MTCCH) may be defined for downlink transmission (forexample, DL-URLLCH, DL-MBBCH and DL-MTCCH) and for uplink transmissions(for example, UL-URLLCH, UL-MBBCH and UL-MTCCH). A type of TrCH maycorrespond to a type of physical data channel, may be associated with aSOM, may be associated with a physical control channel, and/or with aspecific set of DCIs. Different access and procedures may be triggeredas a function of the type of TrCH LCH required by the network/WTRU orfor the type of associated priority/QoS level and/or SOM.

FIG. 6 is a diagram of the example assistance modes 600 available, whichmay be used in combination with any of the embodiments described herein.WTRUs may be connected to TRPs either in standalone mode 609 or assistedmode 610. For example, WTRUs 604 a, 604 b, and 604 c are connected instandalone mode 609, while WTRUs 611 a, 611 b, 611 c, and 611 d areconnected in assisted mode 610. The group of cells that requireassistance may be called the assisted layer 603 and the group of cellsthat provides the assistance may be called the assistance layer 602.

In the example of FIG. 6 , the following assistance modes are shown:

WTRU 611 a connected to 5Gflex small cell in sub-6 GHz band 607 assistedby 5Gflex macro cell in sub-6 GHz band 606;

WTRU 611 b connected to 5Gflex small cell in sub-6 GHz band 607 assistedby LTE-Evo macro cell 605;

WTRU 611 c connected to 5Gflex small cell in above-6 GHz band 608assisted by 5Gflex macro cell in sub-6 GHz band 606;

WTRU 611 d connected to 5Gflex small cell in above-6 GHz band 608assisted by LTE-Evo macro cell 605;

WTRU 611 e connected to 5Gflex small cell in below-6 GHz band 607assisted by 5Gflex small cell in above-6 GHz band 608;

In the example of FIG. 6 , the following standalone modes are shown:

WTRU 604 b connected 612 to 5Gflex small cell in below-6 GHz band 607 instandalone mode;

WTRU 604 a connected 601 to 5Gflex macro cell in sub-6 GHz band 606 instandalone mode; and

WTRU 604 c connected 613 to 5Gflex small cell in above-6 GHz 608 band instandalone mode.

FIG. 7 is a diagram of an example system 700 for initial access usingsystem signatures or signature sequences, which may be used incombination with any of the embodiments described herein. A network maysupport different numerologies, each associated with a specific accessmethod tailored for a specific type of service/use case. Referring toFIG. 7 , WTRU 707 may include the elements of example WTRUs 102 of FIG.1A, FIG. 1B, and FIG. 1C. WTRU 707 may be configured to receive and/ordetect one or more system signatures or system signature sequences.

A system signature may include or comprise a signal structure using asequence. The terms system signature, system signature sequence,signature sequence, and signature may be used interchangeably herein.These system signatures may be similar to a synchronization signal, suchas LTE PSS or SSS. A system signature as used herein may be any type ofsignal received or transmitted by a WTRU, TRP, any other devicedescribed herein, or any other device capable of operating in a wirelesscommunications system, and a system signature may be used in any of theembodiments described herein.

In the example of FIG. 7 , each TRP of a plurality of TRPs each transmita system signature. TRPs 705 a, 705 b, 705 c, 705 d, and 705 e transmitsystem signature A 701, which may, for example, be associated withNumerology A and mMTC services. TRPs 704 a, 704 b, and 704 c transmitsystem signature B 702, which may, for example, be associated withNumerology B and Default Access and eMBB services. TRPs 706 a, 706 b,and 706 c transmit system signature C 703, which may, for example, beassociated with Numerology C and URLLC services. TRPs, such as TRP 704 cin the example of FIG. 7 , may be connected to MME 711 via S1-Cinterface 712 and serving gateway (S-GW) 710 via S1-U interface 713.

A node, such as the TRPs and/or WTRU of FIG. 7 , may transmit and/orreceive one or more system signature on one or more frequency and timeresources. System signatures may occupy the entire bandwidth of anoperating channel or only a portion of the bandwidth. System signaturesmay be transmitted once within a period or multiple times per window.For example, a burst of a signal may be transmitted x times in a windowand not transmitted until a next window occurs. The windows may or maynot overlap. System signatures may occupy either a partial OFDM symbol(for example, transmitted in the guard period or cyclic prefix as aunique word) or occupy one or more OFDM symbols. Different types ofphysical signals may be used as system signatures including but notlimited to the following: synchronization signals, cell or TRP specificreference signals (for example, CRS), reference signals that are commonto a group of TRPs (TRPG), preambles, a unique word, a positioningreference signal, other reference signals, bits in a master informationblock (MIB), bits in a system information block (SIB), any otherbroadcast channel, or a low overhead physical channel that carries a lownumber of payload bits. Such a physical channel may be designed foradditional robustness, for example, with an attached CRC.

System signatures may be specific to a particular node or TRP within agiven area (for example, by uniquely identifying the node), or they maybe common to a plurality of nodes or TRPs within an area. A WTRU mayidentify or distinguish the transmitting node uniquely from the systemsignature. A given system signature may be associated with more than onenode, and a WTRU may use the received system signature toidentify/characterize one or more parameters or operational aspectsassociated with a group of nodes. For example, a system signature may becharacterized as follows:

A system signature may be TRP specific and may be used to identifyand/or distinguish TRPs;

A system signature may be TRPG specific in which a same system signaturefor two or more TRPGs within a layer may identify common accessparameters;

A system signature may be layer specific and may differentiate a macrolayer from a small cell layer;

A system signature may be WTRU specific such as for use in D2Doperation;

A system signature may be relay specific such as for use in relayoperation;

A system signature may be SOM/slice specific. Each SOM/Slice may carryits own system signature. In one example, the system signatureassociated with the SOM/slice may be transmitted using the radioresources (time/frequency resources) and/or parameters (for example,numerology, TTI, CP etc.) specific to that SOM/slice.

Each system signature may be composed of different parts calledsub-signatures. For example, one sub-signature may be antenna portspecific, TRP specific, SOM specific, or specific to plurality of TRPs,etc. Alternatively or additionally, a WTRU may receive more than onedistinct system signature from the transmitter (TRP or another WTRU).

Different types of system signatures may be identified and/ordistinguished by the format of the signals used as signatures. Forexample, synchronization signals may be used as layer specific systemsignatures, whereas positioning reference signals may be used as TRPspecific reference signals.

Different types of system signatures may be defined and/or transmittedin order to support different WTRU capabilities. For example, WTRUsunder normal coverage may receive the whole system signature, whereasWTRUs with enhanced coverage requirements and/or with limited RFbandwidth capability may receive a sub-signature of the whole signatureand obtain partial information associated with the receivedsub-signature. Different sub-signatures of system signatures may beassociated with a different periodicity or repetition factor.

Different sub-signatures and/or distinct system signatures may have apredefined linkage between them. The linkage may be defined in terms ofone or more of the following: a timing relation (for example, symbols,subframes, etc.), a frequency relation (for example, subcarrier mapping,RB offset, etc.), a spatial relation (for example, mapped to differentbeams or different types of beams such as wide beams or narrow beams),aspects of the signal itself (for example, sequence number, orthogonalcode, signal structure used, repetition number), and a different antennaport (for example, TRP specific system signatures from antenna port xand TRPG specific system signatures from antenna port y). A WTRU maydetermine one or more system parameters or a configuration using thelinkage between system signatures and/or sub-signatures.

A WTRU may determine the placement of system signatures in the framestructure and/or resource grid (for example, in time and/or frequencyresources) using a predefined configuration. Alternatively, theplacement of a system signature within the frame structure and/orresource grid may be flexible to avoid interference and to enableforward compatibility. The WTRU may determine this flexible placementfrom a cell specific configuration or in relation to othersignals/channels or provided by an assistance layer (for example, LTElayer) or using a blind detection within a time window. Detection of onesignature may enable detection of other signatures associated with thesame transmitting node (for example, TRP and/or WTRU).

Referring to FIG. 7 , WTRU 707 may support multiple services such asmMTC, eMBB, and URLLC, access methods in support of the multipleservices, and multi-connectivity. WTRU 707 may receive system signatureA 701, system signature B 702, and system signature C 703 and thendetermine one or more parameters associated with a network based on eachsystem signature. For example, WTRU 707 may derive an index from eachsystem signature and may use it to retrieve associated parameters, whichmay for example be retrieved from an access table stored in the WTRU.For example, WTRU 707 may use the received power associated with thesystem signature for open-loop power control, which may be used for thepurpose of setting the initial transmission power if WTRU 707 determinesthat it may access and/or transmit to the system using applicableresources of the system. In another example, WTRU 707 may use the timingof the received system signature or signature sequence for the purposeof setting the timing of a transmission such as a preamble on a PRACHresource if WTRU 707 determines that it may access and/or transmit tothe system using applicable of the system.

WTRU 707 may be configured with a list of one or more entries, which maybe referred to herein as an access table. The access table may be storedin the memory of WTRU 707 as described above, and the access table maybe indexed whereby each entry is associated with a system signatureand/or to a sequence thereof. The entries may be parameters for eachsystem signature. Such entries may include but are not limited to anaccess method (for example, PRACH) numerology aspects (for example, TTIduration), and TRP/G-specific control channel information. Based on thisindex, an entry in the access table may be associated with a pluralityof nodes or TRPs. The WTRU may receive the access table by means of atransmission as described above. This received transmission may usededicated resources, which may for example be by RRC configurationand/or by means of a transmission using broadcasted resources. Whenusing broadcasted resources, the periodicity of the transmission of anaccess table may be relatively long (for example, up to 10240 ms), andit may be longer than the periodicity of the transmission of a signature(for example, in the range of 100 ms). An access table as referred toherein may comprise any type of system information received by WTRU 707for any of the purposes described herein.

The access table may provide initial access parameters for one or moreareas. Each entry in the access table may provide one or more parametersnecessary for performing an initial access procedure with the system.These parameters may include at least one set of one or more randomaccess parameters, which may include but are not limited to applicablephysical layer resources in time and/or frequency (for example, PRACHresources), an initial power level, and physical layer resources forreception of a response. These parameters may further include accessrestrictions, which may include but are not limited to Public LandMobile Network (PLMN) identity and/or CSG information. These parametersmay further include routing-related information such as the applicablerouting area(s).

WTRU 707 may have data available for transmission associated with aspecific service, determine by measurements the detected systemsignatures, determine the access configuration applicable to theservice, and perform a corresponding access procedure using systeminformation associated with the determined access table entry. WTRU 707may then receive at least one random access response (RAR) such as RAR708 or 709 and establish a Uu connection with the system.

FIG. 8 is a flow diagram of an example process for initial access usingsystem signatures or signature sequences 800 that may be performed inthe example system 700 described above and used in combination with anyof the embodiments described herein. While each step of the process 800in FIG. 8 is shown and described separately, multiple steps may beexecuted in a different order than what is shown, in parallel with eachother, or concurrently with each other. The process of FIG. 8 isperformed by a WTRU for exemplary purposes, but it may also be performedby any node operating in a wireless communications system such as a TRP,eNB, 5gNB, AP, or base station. In the example of FIG. 8 , a WTRU, viathe transceiver or receiver of the WTRU as described above, may receivea system signature 801 from at least one TRP of a plurality of TRPs. Thesystem signature may be associated with any of the parameters andcharacteristics described above. For example, the received systemsignature may be associated with a numerology, a network slice, adiscontinuous transmission (DTX) state, a control channelcharacteristic, or a network service.

The WTRU may then determine, with use of a stored access table, aresource selection, an initial access method of a plurality of accessmethods that are specific to the numerology associated with the systemsignature, a network slice, a network service, and/or a group of the atleast one TRP 802. During this step, the WTRU may measure, read, and/ordecode the received system signature and perform one or more actionsrelated to a specific aspect of the system signatures. The relationbetween different sub-signatures, different distinct system signatures,and/or types of signatures sequences may convey one or more aspects ofthe system configuration. The relation may be in the time domain (forexample, symbols or an offset) and/or frequency domain (for example,subcarriers or resource blocks (RBs)). The relation may also includeproperties of the system signature (for example, type, sequence number,or the root sequence). Referring to FIG. 8 , the WTRU may then receiveat least one RAR message from the at least one TRP 803.

During the procedure described in FIG. 8 , the WTRU may determine systemoperation/configurations from the received system signatures includingbut not limited to the following:

The WTRU may determine a logical area with one or more commonaspects/properties. The WTRU may assume that a group of TRPs with thesame system signature uses a common system configuration (for example,initial access parameters). The group of TRPs may belong to the samesignature area or common SIB area within which the WTRU may notreacquire the system information upon TRP change. In some embodiments,the WTRU may see the group of TRPs as a single TRP or a logical cell.The WTRU may assume that the group of TRPs with the same systemsignature is associated with the same central unit. The WTRU may forexample perform layer2 re-establishment within the TRPs associated withthe same central unit instead of layer3 re-establishment.

The WTRU may determine a pointer to an entry in a global systeminformation table. The WTRU may apply the system information (forexample, initial access parameters including a PRACH configuration,etc.) in the access table associated with or indexed by that systemsignature or parts of the system signature. Also, when the WTRU nolonger receives a system signature or parts of a system signature, theWTRU may cease to use the current system information associated withthat system signature or parts of the system signature.

The WTRU may determine a mapping to a pre-defined broadcast RNTI. TheWTRU may start to monitor control channels for a pre-defined broadcastRNTI associated with that system signature. The broadcast RNTI may thenbe used to schedule system information and/or an access table associatedwith that system signature.

The WTRU may determine support of a service (for example, eMBB, MMTC,ULLRC) or parts of a system signature or a group of reserved systemsignature sequences that may indicate support of specific service. Forexample, system signature 1 may indicate support of eMBB, signature 2may indicate support of MMTC, and signature 3 may indicate support forULLRC. Alternatively, a relation between system signatures or parts ofsystem signatures may convey the same information.

The WTRU may determine support of a SOM by using a system signature thatmay be associated with a plurality of SOMs. The mapping between a SOMand a system signature may be pre-defined or indicated as a part of theaccess table information. The WTRU may determine the presence of one ormore SOMs within the frame structure based on the presence of one ormore system signatures associated with those SOMs.

The WTRU may determine the DTX state of the network. Each TRP in thenetwork may be in one of the various DTX states or visibility levels.For example, completely OFF, transmitting only system signatures, CRS isOFF, CRS is ON, periodic transmission of access tables, on-demandtransmission of access tables, transmitting access tables for highpriority services (for example, emergency calls), etc. The WTRU maydetermine the DTX state of the TRP from the system signaturestransmitted by the TRP. One or more system signatures may not directlyprovide system information, and rather they may point to specific ULresources that may be used to activate the system information. The WTRUmay request the transmission of access tables using those UL resources.In one embodiment, WTRUs may be configured to report the TRPs in DTX(for example, using reserved system signatures). The network maydetermine the activation of TRPs based on a number of WTRU reports.

The WTRU may determine paging via system signatures. Pre-defined systemsignatures may be used for the paging procedure. This may include thepresence of a paging message for one or more WTRUs to be indicated via apre-defined system signature. Such an indication may be of differentlevels, which may be for example a frame level or subframe level.Time/frequency resources for actual paging message transmission may beindicated via a predefined signature, and such resources may, forexample, be defined in the access table. UL time/frequency resources fora paging response/preamble transmission may be indicated via apredefined system signature, and such resources may be defined in theaccess table.

The WTRU may determine an indication of an association with a specificnode in the assistance layer. The WTRU may consider one or more TRPs inan assisted layer transmitting same system signatures to be associatedwith the same node in the assistance layer. For example, a group of5Gflex TRPs transmitting a same reference signal may be associated withthe same LTE-Evo macro eNB. The WTRU may determine the specific LTE-Evomacro eNB.

The WTRU may determine an indication of a control channelcharacteristic/property that may be used. The WTRU may determine one ormore of the following characteristics/properties associated with thecontrol channel from the system signature:

Type of control channel: the WTRU may determine the type of controlchannel based on the system signature. For example, the WTRU maydetermine the presence of a control channel associated with more thanone TRP based on the presence of a predefined system signature.Similarly, the WTRU may determine the presence of a TRP specific controlchannel based on the presence of a TRP specific system signature. TheWTRU may determine the presence of a SOM/slice specific control channelbased on the presence of a system signature specific to that SOM/slice.The WTRU may determine whether the control channel is beamformed or notbased on a presence of a predefined system signature. The WTRU maydetermine the presence of an enhanced coverage control channel (forexample, with repetition in time and/or frequency) based on the presenceof a pre-defined system signature.

Location of the control channel: WTRU may obtain the location of thecontrol channel based on the relative location of the system signature.For example, the control channel may be placed at a predefined offset interms of time (for example, symbols) and/or frequency (for example,sub-carrier offset, RB offset, etc.)

Length/size/bandwidth of the control channel: the WTRU may determine thesize of the control channel (for example, in terms of a number of OFDMsymbols) as a function of the system signature. For example, apredefined mapping may exist between the system signature sequence and anumber of OFDM symbols carrying the control channel. Similarly, the WTRUmay determine the bandwidth of the control channel either explicitlybased on a pre-defined system signature or implicitly based on resourcesoccupied by the system signature.

The WTRU may determine an identity related to the TRP or TRPG. The WTRUmay identify and/or distinguish a TRP from other TRPs based on thereceived system signature. A WTRU may identify two or more TRPs beingpart of the same group based on the presence of a common systemsignature. The WTRU may identify and/or distinguish a TRPG from otherTRPGs based on the received system signature. The WTRU may consider aTRP belonging to two or more TRPGs when it receives two or more TRPGspecific system signatures from the same TRP. In some embodiments, asystem signature may comprise two or more parts, for example a firstpart that is TRPG specific and a second part that is TRP specific.

The WTRU may determine a specific network slice wherein each RAN sliceis associated with a set of radio resources, which may be dedicated orshared with other RAN slices. The WTRU may identify the parts of radioresources associated with a specific RAN slice based on the presence ofa system signature associated with that slice. In one example, the WTRUmay determine the bandwidth allocated to a specific RAN slice based onthe bandwidth occupied by the system signature associated with thatslice or based on a function of system signature sequence associatedwith that slice. The WTRU may determine if the one or more subframesand/or TTIs and/or OFDM symbols are associated with a specific RAN slicebased on the presence of a predefined system signature in thosesubframes and/or TTIs and/or OFDM symbols. The WTRU may obtain themapping between the system signatures and associated RAN slice, whichmay be for example, obtained from an access table or a WTRU specificconfiguration. Similar mechanisms may be used to associate a SOM or asignal structure with a system signature.

The WTRU may determine a specific numerology. This may includesituations where the WTRU determines one or more parameters associatedwith the numerology as a function of the system signature. For example,the one or more parameters associated with the numerology may includebut are not limited to: TTI length, number of symbols per TTI,bandwidth, subcarrier spacing, and cyclic prefix. In one example, a setof supported or allowed numerology configurations may be predefined andmapped to unique system signatures using an access table.

The WTRU may determine a specific frame structure that may be used. Forexample, the WTRU may determine the duplex mode or a frame structuretype based on the received system signature. For example, a predefinedsystem signature may be reserved to indicate one of TDD duplex mode, FDDduplex mode, half duplex mode, or full duplex mode, etc. The WTRU mayadditionally determine the type of one or more physical channels withina frame structure as a function of the presence of predefined systemsignatures. For example, a first symbol in a subframe may carry asignature that describes the rest of the frame, whether the frame isalmost blank or if the frame is self-contained (i.e. there is supportfor transmissions in both the uplink and downlink multiplexed in timewithin the same subframe) and a specific format of the self-containedframe (i.e. DL control and/or data followed by UL control and/or data,UL data and/or control followed by DL control and/or data, etc.).Similarly, the WTRU may determine the subframe number, slot number,system frame number, etc. as a function of the system signature.

The WTRU may determine an indication of the networkcapabilities/features that may be used. For example, in legacy systems,the WTRU may be required to decode system information to determine thenetwork capability, i.e. if the network supports one or more features.In next generation systems, the WTRU may directly determine one or morenetwork capabilities based on the presence of one or more systemsignatures. This may reduce the latency and overhead, as the WTRU maynot be required to receive and decode the system information from eachTRP. For example, predefined system signatures may be reserved toindicate support for eMBMS, D2D, above 6 GHz carrier, etc. Additionally,a first group of system signatures may be reserved to indicate thenetwork support of an initial set of 5G features (for example, phase1)and a second group of signatures may be reserved to indicate networksupport of an extended set of 5G features (for example, phase2). In oneexample, WTRUs with phase2 capability may perform preferential accesstowards TRPs with the second group of signatures.

The WTRU may determine a specific deployment or mode of operation thatmay be used. The WTRU may distinguish between the LTE-assisted 5GFlextransport channels and the standalone 5GFlex operation based on systemsignatures. Predefined system signatures may be placed in an LTE framestructure to indicate the presence of one or more 5GFlex physicalchannels. Similarly, a different set of system signatures may indicate astandalone 5GFlex operation. WTRU logic to perform initial access may bea function of the system signatures that are received within a frame.The WTRU may differentiate between a macro TRP and a low power TRP basedon the predefined system signature transmitted from the TRPs.

The WTRU may determine the suitability of the TRP or TRPG. The WTRU maydetermine the suitability of a TRP or group of TRPs using a qualitymetric based on measurements performed using a system signature. Suchmeasurements may be used for selection of TRP/TRPGs for initial access,for handover, or to perform idle mode paging monitoring.

The WTRU may determine a specific version (with respect to a predefinedset of information) of system information that may be used. Each systemsignature may be associated with a predefined set of system information.Upon reception of such a system signature, the WTRU may apply theassociated configuration in the system information.

The WTRU may determine the size and the format of the initial accessmessage (e.g., msg1, msg3 etc.) as function of a system signature.

The WTRU may determine that the timing of system signatures may be usedas a DL timing reference.

The WTRU may determine that the received power of system signatures maybe used as DL pathloss references.

The WTRU may determine the location of an access table based on thereceived system signature. For example, the WTRU may determine thepresence and format of a data channel carrying the access table based onthe system signature. The WTRU may not need to know or decode thecontrol channel in order to receive the access table information. Theaccess table information may be, for example, transmitted with apredefined MCS. In one example, the WTRU may determine the redundancyversion for the access table transmission using the received systemsignature.

The WTRU may determine linked bands/DL/UL frequencies (for example, therelation between system signature and placement and bands of operation).

The information contained in the transmission of system information maybe structured in a specific manner. For example, such information may bereceived as a list of elements. Each element may represent a modularelement, for example, in the access table. System information in theaccess table may be grouped into different sub-tables.

The information in such elements may be grouped based on characteristicsincluding but not limited to the following:

Specific to a physical node: for example, a TRP specific sub-table, TRPGspecific sub-table. For example, the WTRU may determine that parametersassociated with one such element may be associated with theconfiguration a distinct and/or dedicated MAC instance.

Specific to a RAN slice: for example, the WTRU may determine thatparameters associated with one such element may be associated with theconfiguration and/or availability of one or more specific type(s) ofprocessing (for example, L1, L2) and/or a specific type and/or level ofsupported QoS.

Specific to a service (eMBB, ULLRC, mMTC): for example, the WTRU maydetermine that parameters associated with one such element may beassociated with the configuration and/or availability of one or morespecific type(s) of control channel, physical data channel (uplinkand/or downlink), and/or type of supported QoS.

Specific to a SOM: for example, the WTRU may determine that parametersassociated with one such element may be associated with theconfiguration and/or availability of one or more specific type(s) and/orset of physical resources.

Specific to a feature/capability (for example, MBMS, D2D, and the like):for example, the WTRU may determine that parameters associated with onesuch element may be associated with the configuration and/oravailability and/or support for one or more specific types of (forexample, WTRU-related) capabilities or combinations thereof. Forexample, the WTRU may determine that one or more sets of features aresupported by the network using the associated access parameters.

Specific to a layer (for example, macro sub-table, small cellsub-table): for example, the WTRU may determine that parametersassociated with one such element may be associated with theconfiguration and/or availability and/or support for one or morespecific types of radio access method(s), which for example, may bebased on system information broadcasts and RRC connectivity,signature-based access, or other methods.

Specific to a component carrier (Pcell sub-table, PScell sub-table,Scell sub-tables): for example, the WTRU may determine that parametersassociated with one such element may be associated with theconfiguration and/or availability and/or support for one or morespecific types of aggregation of radio resources. For example, an accessmethod whereby the outcome of the L1 access (for example, preambletransmission and/or random access) may result in a plurality ofassociations each with different carriers and/or TRPs.

Group IEs: Group IEs that are cell specific separately from IEs that arelayer specific (or common to more than one TRP).

Specific to a mobility set and/or an access set (for example, to a groupof one or more TRPs that share at least some aspects): such aspects mayinclude procedures and/or functions such as, for example, support forcoordinated scheduling, COMP, carrier aggregation, MBMS area, commonaccess rights, seamless mobility within TRPs of such a group, commonsecurity context, WTRU context availability/sharing for all TRPs of sucha group, and the like. For example, this may be applicable when all TRPsin a set are controlled by the same central entity and/or are connectedto each other and/or to the central control entity by interfacesenabling such coordination (for example, an ideal interface). Forexample, the WTRU may determine that parameters associated with one suchelement may be associated with the configuration and/or availability ofone or more specific procedure(s), for example, such as L1/PHY mobility.

Specific to a type of radio access technology (for example, LTE,5gFLEX): for example, the WTRU may determine that parameters associatedwith one such element may be associated with the configuration and/oravailability and/or support for one or more specific types of radioaccess and/or access methods. For example, the WTRU may determine thatthe associated radio access procedure uses legacy LTE methods (or anevolution thereof) for standalone access. For example, the WTRU maydetermine that the associated radio access procedure uses the 5gFLEXprocedures for standalone access. For LTE CP/PHY+5gFLEX PHYsuperposition, DC or CA, for example, the WTRU may determine that theassociated radio access procedure uses legacy LTE methods (or anevolution thereof) such that the WTRU may first establish an RRCConnection for the subsequent configuration of one or more 5gFLEXTrCH(s) and/or physical data channel(s). The WTRU may possibly furtherdetermine whether such a configuration is for the same carrier (forexample, by superposition of additional physical channels), a differentcarrier (for example, by carrier aggregation principles) and/or separateMAC instances (for example, using different schedulers by dualconnectivity principles). For LTE CP+5gFLEX PHY substitution, forexample, the WTRU may determine that the associated radio accessprocedure uses legacy LTE methods (or an evolution thereof) for theL3/RRC Control Plane following an access using the 5gFLEX procedures,for example—based on 5gFLEX access tables, signature detection,transmission over 5gFLEX TrCH(s), and/or physical access/datachannel(s). These elements may be further grouped together respectively.Such groups may be further separated from each other.

FIG. 9 is a flow diagram of an example process for detecting/acquiringsystem information via access tables 900 that may be performed in theexample system 700 described above and used in combination with any ofthe embodiments described herein. While each step of the procedure 900in FIG. 9 is shown and described separately, multiple steps may beexecuted in a different order than what is shown, in parallel with eachother, or concurrently with each other. The process of FIG. 9 isperformed by a WTRU for exemplary purposes, but it may also be performedby any node operating in a wireless communications system such as a TRP,eNB, 5gNB, AP, or base station. In the example of FIG. 9 , a WTRU, viathe transceiver or transmitter of the WTRU as described above, maytrigger a procedure to acquire or reacquire at least one access table901 based on a received system signature, an aspect associated with thevalidity of a previously received access table, for pre-acquisition ofan access table, upon power up, and/or upon expiration of a timer.

For example, the WTRU may receive a system signature periodically tostay up to date with the system configuration. The WTRU may trigger aprocedure to acquire or reacquire the at least one access table 901 whenthe WTRU receives an unknown system signature. For example, the WTRU maydeclare a received system signature as unknown when the WTRU does nothave a valid access table associated with the system signature stored inits memory. If the WTRU receives an unknown system signature, it mayperform actions including but not limited to the following: reportingthe unknown system signature to the currently associated TRPs or TRPGsand/or reporting the unknown system signature to the assistance layer,triggering an on-demand access table transmission procedure, orconsidering the unknown system signature as being from inaccessibletransmitter.

In another example, the WTRU may trigger a procedure to acquire orreacquire the at least one access table 901 when the WTRU receives areserved signature, which is special signature that may be reserved toindicate a change in the access table.

In another example, the WTRU may trigger a procedure to acquire orreacquire the at least one access table 901 when the WTRU determinesthat a measurement related and/or associated with a system signatureand/or to the reception of an access table is no longer of sufficientquality. In this example, the validity of an access table may be afunction of a reception quality of the transmitted access table.

In another example, a WTRU may trigger a procedure to acquire orreacquire the at least one access table 901 after determining that oneor more entries in the stored access table are no longer valid. Thevalidity of the access table may be determined by a change in a valuetag when the value tag associated with the stored access tableinformation is different from the network broadcasted value tag. Thevalue tag may be defined at different levels of granularity. The valuetag may be associated with a whole access table, and/or sub-table,and/or group of entries, and/or a specific entry in the table. Whenreacquiring an access table, the WTRU may reacquire only the relevantportion of the access table according to the granularity of the valuetag. The WTRU may receive the value tag used to determine the validityof the access table in several ways, including but not limited to thefollowing: as a separate entry in the access table, in a MAC controlelement, in a physical channel reserved to carry value tag information,using one or more properties of the synchronization channel ordemodulation reference signal, and/or in a paging message.

In another example, a WTRU may trigger a procedure to acquire orreacquire the at least one access table 901 via pre-acquisition of theaccess table. In this example, the WTRU may pre-acquire the access tableassociated with one or more system signatures, before actually receivingthe one or more system signatures. WTRU may pre-acquire the access tableusing one or more of the following methods:

The WTRU may determine the need to acquire or re-acquire the accesstable based on its location and proximity to one or more systemsignatures. For example, the WTRU may be configured with a list ofsystem signatures that are active in a geographical location defined bythe location area, routing area, RAN area, or relation based onpositioning reference signals, or other means to obtain locationinformation (for example, GPS/GNSS).

As part of handover information, the WTRU may receive a list of accesstables from the source cell, which may correspond to one or more systemsignatures in the target cell.

The WTRU may receive parts of access table information during aconnection release procedure. The WTRU may use the access tableinformation in the idle mode for example.

The WTRU may pre-acquire access table information associated with one ormore system signatures that are turned off. These system signatures maycorrespond to one more TRPs in a DRX state and/or one or more inactiveservices within the active TRPs.

In another example, a WTRU may trigger a procedure to acquire orreacquire the at least one access table 901 upon power up. In thisexample, the WTRU may acquire the access table upon power up when, astored access table is empty, and/or the WTRU does not have a validaccess table associated with the received signature.

In another example, a WTRU may trigger a procedure to acquire orreacquire the at least one access table 901 upon expiry of a timer. Inthis example, the WTRU may acquire or re-acquire the access table uponexpiry of a periodic refresh timer.

After triggering a procedure to acquire or reacquire the at least oneaccess table 901, the WTRU may receive the at least one access table902. The WTRU may detect and receive the at least one access table thatincludes system information using several methods. For example, accesstable transmissions may be associated with a separate logical channeland be mapped to a transport channel that may include one or more of thefollowing transmission characteristics:

The periodicity of the transmission of an access table may be relativelylong (for example, up to 10240 ms). The periodicity also may be longerthan the periodicity of the transmission of a system signature (forexample, in the range of 100 ms).

Different parts of the access table (for example, sub-tables) may betransmitted with different periodicity based on the order of importanceto regular WTRU operation. For example, a sub-table carrying informationregarding the accessibility/PLMN information or initial accessinformation may be transmitted more frequently than others.

Various modes of access table transmission may also be implemented. TheWTRU may receive the access table information associated with anassisted layer from the assistance layer. For example, the WTRU mayreceive the access table information for a 5gFLEX small cell layer froma LTE-Evo macro cell using methods including but not limited to thefollowing: a type of system information in the assistance layer (forexample, a SIB in the macro cell for the group of small cells/TRPG), aSC-PTM mode in the assistance layer, and/or a shared data channel (e.g.,PDSCH) as dedicated WTRU information. In another example, the WTRU maycombine transmissions from the assistance layer and assisted layer toform the complete access table. For example, WTRU may receive a baselineaccess table from the LTE macro layer and only the delta changes on topof the baseline table from the 5gFLEX small cell layer.

For multi-TRP coordinated broadcast mechanisms (single frequency mode),the WTRU may receive the access table information from more than one TRPon the same time/frequency resource. The WTRU may consider such accesstable information being applicable to more than one TRP, which may beover a geographical region. A separate antenna port may be defined foraccess table transmission. The WTRU may perform layer mapping andprecoding assuming that a single antenna port is used. The access tabletransmissions may use an extended cyclic prefix. Multi-TRP coordinatedbroadcast channel may be associated with a dedicated reference signalthat is different from a cell specific reference signal.

For TRP specific transmission, an access table may be transmitted withinthe coverage of a single cell/TRP using a shared or common data channelor broadcast channel. The downlink control messages corresponding toaccess table transmissions may be identified by a reserved RNTI. Forexample, at least two RNTIs may be used to identify different sub-tablesof an access table. Alternatively, the access table may be transmittedusing a Single Cell Point to Multipoint transmission (SC-PTM) within aTRP.

A hybrid mechanism may also be implemented for transmission of an accesstable. The WTRU may receive RAN area/layer specific parts of an accesstable using a multi-TRP mechanism, and cell specific parts of an accesstable may be received via a broadcast or unicast mechanism. For example,the WTRU may differentiate the modes of transmission as a function ofsystem signatures. For example, different system signatures may bereserved for a specific mode of access table transmission.

Access table transmissions may be multiplexed with other logicalchannels in the same subframe/TTI. Access table transmissions may alsobe self-contained, i.e. associated with a dedicated synchronizationsignal and/or a demodulation reference signal. The resource elementscarrying the demodulation reference signal may be time and/or frequencymultiplexed with the resource elements carrying the access tableinformation. The WTRU may obtain time and/or frequency synchronizationusing the synchronization signal dedicated for access table acquisition.Some examples of the synchronization signals include but are not limitedto preambles and/or sequences, functions of system signatures, orpredefined sequences reserved for an access table, unique word, etc. Inanother example, the dedicated synchronization signal may be differentfrom a cell specific synchronization signal. The dedicatedsynchronization signal may transmit on demand, i.e. transmitted onlywhen there is an associated access table transmission active. Thesynchronization signal may be located at an offset from the access tabletransmission. The WTRU may detect the presence of the access table fromthe presence of a dedicated synchronization signal associated with theaccess table transmission. The maximum transport block size for anaccess table transmission may be restricted to be less than a thresholdto accommodate different WTRU capabilities. WTRUs in coverage limitedscenarios or RF bandwidth restricted scenarios may receive additionalrepetitions of access table transmissions to increase SNR androbustness.

After receiving the at least one access table 902, the WTRU may storethe at least one access table 903 associated with one or more systemsignatures in memory. The memory of the WTRU may include but not is notlimited to non-removable memory 130, removable memory 132 describedabove with respect to FIG. 1B. When storing the at least one accesstable 903, the WTRU may store a base line configuration, which hascommon values for most of the system, parameters and then may only storethe delta configuration for each system signature. Additionally, theWTRU may receive a long term configuration that may be WTRU specific, tobe used in cells/TRPs where the WTRU visits frequently.

Assuming that the WTRU memory may hold access tables corresponding atmost n system signatures, the WTRU may use one or more of the followingalgorithms to make room for an access table corresponding to a newlyreceived system signature when its memory is full (already holding nsignatures):

The WTRU may keep track of how often the access table information wasretrieved for each system signature. The WTRU may overwrite the nth mostfrequently used system signature memory with the newly received systemsignature.

The WTRU may keep track of the time spent (or time of stay) in eachcell/area associated with the signature. The WTRU may overwrite thesystem signature where the least amount of time was spent with the newsignature.

The WTRU may keep track of most recently received system signatures. TheWTRU may overwrite the least recently used system signature with the newsystem signature.

The WTRU overwrite the oldest signature (in terms of when it was writteninto the memory) memory with the new signature information (i.e. Firstin First Out).

Before initiating the procedure 900 of FIG. 9 to acquire or re-acquirean access table, the WTRU may first determine that it has access rightsto the cell (e.g., PLMN ID, CSG, access barring etc.). The WTRU may thenensure that it has valid initial access parameters associated with thesystem signature(s), before any uplink transmission in the cell. Theseparameters may be provided by one or more entries in the access table.

The WTRU may determine the transmission characteristics of the accesstable including the resources used for access table transmission interms of time, frequency, space and/or code, using one or more of thefollowing methods:

The WTRU may determine that scheduling modes for the access table may beperiodic or on-demand. For a periodic scheduling mode, parts of theaccess table may be transmitted at a predefined periodicity. Forexample, only the absolute minimum required for initial WTRU access maybe transmitted periodically. In this example, only the UL resourceconfiguration for initial access PLMN ID, Access restriction,Non-critical extensions etc., may be transmitted. Such periodictransmissions may not be limited to just one TRP and may be commonparameters applicable to two or more TRPs. The on-demand solution may beconsidered as a leaner approach compared to sending all the systemparameters for all TRPs all the time. Parts of an access table may notbe transmitted periodically and only transmitted based on a request bythe WTRU. A WTRU triggered activation of the access table transmissionmay include WTRUs requiring access table information be configured totransmit an explicit access table activation request/interestnotification message. The WTRU may use UL resources reserved to triggeron-demand access table transmissions. (e.g., UL RACH resources or ULsignal). In an example, the WTRU may request specific parts of theaccess table by transmitting detected a system signature and/or a valuetag and/or a reason/cause code. The WTRU may receive a RAR relatedmessage that carries a DL grant carrying the requested access tableinformation. There may be timing relations between on-demand requestsand SIB transmission (with or without PDCCH). Alternatively, the WTRUmay receive a paging like message that carries information about theon-demand access table transmission. Such a paging mechanism may bebeneficial for WTRUs to receive the access table opportunistically (i.e.WTRUs that did not transmit an access table request). In a hybridscheduling mode, the access table transmission may dynamically switchbetween on-demand and periodic modes. The hybrid method may allow aflexible periodicity for the access table transmission ranging fromfrequent transmission to completely on-demand transmission. Theperiodicity may be determined by the number of WTRU requests (forexample, WTRUs may be configured to report TRPs in DTX using reservedsignatures), network listening (for example, TRPs may listen to otherTRP transmissions or WTRU transmissions), based on cell load (forexample, it may be efficient to do periodic transmission if the numberof WTRUs in the cell are high), based on assistance layer, based onactive SOM/Services, based on inter-TRP coordination (e.g., over X2),based on RRM aspects (e.g., resource utilization, time of day etc.),etc.

The WTRU may determine the DL resources for access table transmissionbased on one or more of the following methods:

A paging related message that indicates the presence of access tableinformation. Additionally, the paging message may also carry DL resourcegrant with the scheduling information of access table transmission.

A downlink control information (DCI) in a control channel (for example,PDCCH, EPDCCH etc.).

An implicit relationship to the time/frequency resources occupied by thesystem signature, and a dedicated control channel common to a pluralityof TRPs (for example, for single frequency mode of transmission).

The WTRU may request one or more parts of the access table that containsparameters related to a particular connection procedure. The network maythen, in addition to transmitting the requested connection procedureparameters, allocate resources for connection procedure (i.e. piggybackthe access table request and connection request procedure).Alternatively, the WTRU may include specific reasons for a connectionrequest (for example, MO data or signaling), and the network may thenprovide the relevant SIB to the WTRU and additionally allocate resourcesfor the connection procedure. Additionally, the WTRU may include a valuetag in the connection request.

FIG. 10 is a flow diagram of an example random access procedure usinginitial access using system signatures or signature seqeunces 1000 thatmay be performed in the example system 700 described above and used incombination with any of the embodiments described herein. While eachstep of the procedure 1000 in FIG. 10 is shown and described separately,multiple steps may be executed in a different order than what is shown,in parallel with each other, or concurrently with each other. Theprocess of FIG. 10 is performed by a WTRU for exemplary purposes, but itmay also be performed by any node operating in a wireless communicationssystem such as a TRP, eNB, 5gNB, AP, or base station.

In the example of FIG. 10 , a WTRU, via the transceiver or receiver ofthe WTRU as described above, may receive at least one set of RACHconfigurations via an access table 1001 received in accordance with anyof the methods described herein. As a result, the WTRU may be configuredwith one or more sets of potential RACH configurations via the accesstable. RACH configurations may include a preamble configuration (forexample, number of preambles, preamble grouping, preamble selectioncriteria, etc.), power ramping parameters, RAR window configuration,retransmission configuration, PRACH configuration (for example, RACHoccasion, time/frequency resources, RACH format, etc.), retransmission,etc. Additionally, the WTRU may distinguish two different categories ofRACH configurations, which may each be associated with one TRP orassociated with a plurality of TRPs.

The WTRU may receive a system signature 1002. The WTRU may thendetermine the allowed RACH configurations of the at least one set ofRACH configurations based on the received system signature 1003. In someembodiments, the WTRU may select a subset of RACH configurations among aplurality of allowed RACH configurations based on criteria including butnot limited to the following:

The trigger for random access: the WTRU may determine the RACHconfiguration based on whether the msg3 has signaling or data PDUs. EachSOM may be associated with a specific RACH configuration. The WTRU maydetermine the RACH configuration according to the SOM for which the databecomes available. Each network slice may be associated with a specificRACH configuration. The WTRU may determine the RACH configurationaccording to the slice for which the data becomes available.

WTRU state: the WTRU may be in the ACTIVE/CONNECTED state. For example,the WTRU may be already connected to the network and upon wake up fromDRX, the WTRU may select the RACH configuration associated with theserving TRP. Alternatively, the WTRU may perform a RACH procedure inresponse to a network trigger (for example, RACH order). In this case,the WTRU may determine the network node that triggered the RACH orderand select the RACH configuration associated with the network node. TheWTRU may be in the PASSIVE/IDLE state. For example, the WTRU may have noactive connections to the network node and/or during a network nodeselection procedure. The WTRU may select a RACH configuration associatedwith multiple TRPs and perform TRP selection based on RACH procedure.

WTRU coverage status: the WTRU may choose a RACH configuration based onits coverage status, for example normal coverage or needing enhancedcoverage.

Measurement results: the WTRU may select one or more TRPs based onmeasurements on one or more system signatures and/or reference signals.The WTRU may then determine the RACH configuration associated withselected TRPs.

WTRU capability: the WTRU may receive different RACH configurationsindicative of network node capability. For example, a WTRU with expandedfeatures such as a phase2 5G WTRU may prioritize a RACH configurationassociated with TRPs with 5G phase2 capability, whereas a WTRU withlimited features such as a phase1 5G WTRU may select RACH configurationsassociated with LTE assisted TRPs.

DL path loss.

Size of data and/or signaling PDU (for example, MSG3).

The WTRU may be preconfigured with different RACH resource sets, andeach set associated with one of more of the following properties: TRPspecific RACH resources reserved for a point to point RACH procedure;RACH resources specific to two or more TRPs reserved for a point tomulti-point RACH procedure. The multi-point RACH resource configurationmay include whether the WTRU waits for a first RAR (in the case of TRPcoordination) or whether the WTRU waits for the whole RACH window (incase of WTRU based RAR selection).

Referring to FIG. 10 , the WTRU may then transmit a preamble using thereceived system signature 1004. For example, during preambletransmission, the WTRU may use the system signatures for initial powersetting and timing reference (for example, a measurement based on thereception of the system signature). The WTRU may indicate some form ofthe identity of the WTRU using the Msg1/Preamble transmission, whereinthe WTRU ID may be one of: ID of the WTRU specific to a serving TRP (forexample, RNTI); ID of the WTRU specific to a group of TRPs (for example,allocated by a central unit); RNTI of the WTRU allocated in theassistance layer (for example, in the LTE-Evo macro eNB); temporary NASidentifier of the WTRU; and an Explicit RAN level WTRU contextidentifier (for example, unique within a logical RAN area).

Preamble selection and/or PRACH resource selection for use in thepreamble transmission may be a function of the WTRU ID. The WTRU mayselect the preamble and RACH resource based on a hashing function. Thehashing function may map the WTRU ID to a specific PRACH resource. Thenumber of WTRUs may typically be greater than available PRACH resourcesand may result in a collision. A WTRU may randomize the collision byusing, for example, one or more following parameters as input to thehashing function: WTRU identity, an ID related to time domain (forexample, subframe number, symbol number where the RACH is transmitted),an ID related to frequency domain (for example, starting subcarrierindex, RB number, bandwidth region, etc.), cell ID/System signature, andretransmission count.

The WTRU may transmit additional information along with the PRACHtransmission. For example, the WTRU may attach a small payload or MACcontrol element along with the RACH preamble transmission that carriesadditional information such as an explicit WTRU ID or WTRU contextidentifier. In another example, the WTRU may convey additionalinformation by selection of a specific RACH resource. For example, theWTRU may select RACH resources associated with multiple TRPs to conveythe need for network node selection. In another example, the WTRU mayselect a RACH configuration associated with resource repetition toconvey the need for enhanced coverage. In yet another example, the WTRUmay transmit an indication of the WTRU's needs (for example, size of thedata packet, type of service, type of signal structure requested).

The preamble transmissions of the WTRU may be associated with a DLsystem signature, which may be associated with one or more MAC instancesin the network. The RACH resources (for example, time, frequency,preamble, etc.) may be associated with one TRP or group of TRPs. TheWTRU may determine the RACH configuration associated with a signaturefrom the access table. Alternatively, parts of the RACH configurationmay be implicitly determined by one or more aspects of the systemsignature itself (for example, relative offset in time/frequency,bandwidth, etc.).

The WTRU may be configured with a common RACH configuration irrespectiveof the number of TRPs listening to a RACH on those resources. The WTRUmay be transparent to the number of network nodes that receive andprocess the UL random access message.

In another example, the WTRU may indicate to the network if the RACH istargeted towards one TRP or multiple TRPs. The WTRU may provide such anindication by either including additional information with the PRACHtransmission, for example, a MAC control element and/or attaching aunique word to an OFDM symbol and/or as a small payload and/or selectionof RACH resource group and/or preamble and/or time/frequency resourceselection.

The retransmission behavior of the WTRU may be a function of the RACHresource selection. For example, each RACH resource set may beassociated with a different retransmission characteristics/parametersincluding but not limited to the maximum number of retransmissionsallowed, a length of the response window, a contention resolution timer,etc. The WTRU may apply different RACH configurations forretransmissions compared to initial transmission. The WTRU may beconfigured with additional RACH opportunities for retransmission. Forexample, the WTRU may consider additional pre-configured RACH resourcesfor transmission, which may be reserved for retransmission only. TheWTRU may select a RACH configuration associated with multiple TRPs aftera preconfigured number of attempts on a TRP specific RACH have expired.For example, the initial transmission of the WTRU may be specific to aTRP, and upon failure (for example, no RAR or contention resolutiontimer expiry), the WTRU may target the retransmission to more than oneTRP to increase possibility of a success.

Referring to FIG. 10 , the WTRU may receive at least one RAR messagecorresponding to the preamble transmission 1005. The WTRU may receive aRAR corresponding to each RACH transmission. RARs from the same TRP (forexample, to provide enhanced coverage) or RARs from different TRPs (formulti-connectivity) may be separated in time and/or frequency, butwithin a predefined RAR window. The WTRU may be required to receive allpossible RARs within the RAR window and not stop after the first RAR.The RAR window size may be function of number of TRPs involved in theRACH procedure. Or a default RAR window size may be defined and a bitmapin RAR indicate that it is the last RAR message within the window. TheWTRU may also receive different RAR messages (formats/contents) based onselection of RACH configuration. The WTRU may receive informationincluding but not limited to the following in the RAR message:

The WTRU may receive a synchronization signal specific to TRP in the RARmessage. The WTRU may perform synchronization with thepreferred/selected TRP based on the synchronization signal receivedwithin the RAR from that TRP. WTRU may consider the received RAR messageas a DL timing reference for initial access towards that TRP.

The WTRU may receive a TRP identity or an identity specific to group ofTRPs in the RAR message.

The WTRU may receive a number of allowed associations in the RARmessage. The WTRU may limit the max number of associations according toa value signaled in the received RAR message.

The WTRU may receive a reference signal for measurement and selection ofTRPs in the RAR message. The WTRU may use either a combination ofmeasurements made on system signatures and reference signals included inthe RAR or the measurements made on reference signals included in theRAR for selection of TRP(s)

The WTRU may receive a last RAR indication in the RAR message. If thelast RAR indication is false, the WTRU may wait for one or more RARmessages within the current RAR window else the WTRU may stop listeningto RAR messages and assume an end of the RAR window at the subframecarrying the RAR message with last RAR indication as true. Upon the endof the RAR window, the WTRU may perform initial access procedures basedon received RAR messages within the window.

The WTRU may receive additional system information in the RAR message.For example, the RAR message may explicitly include a dedicatedconfiguration to perform further initial access or a connectionestablishment procedure. Alternatively, the RAR message may implicitlyindicate such a configuration via additional signatures or a DCI for thetransmission of additional system information.

The WTRU may transmit additional context information if the RAR messageincludes a request for additional WTRU context information. This mayhappen for example, when the WTRU context cannot be retrieved or isunknown from the preamble or the WTRU ID is ambiguous (i.e. there existsmore than one WTRU context for a given WTRU ID).

The WTRU may receive a redirection message that may be included in theRAR message. For example the WTRU may be redirected to a different TRPwhich was turned OFF earlier and/or redirected to different layer (forexample, a macro layer or small cell layer), different RAT (for example,to a sub 6 GHz or above 6 GHz RAT) or a different spectrum (for example,unlicensed spectrum). The redirection message may additionally provideassistance information, such as timing assistance (for synchronizationto redirected TRP), initial access assistance (for example, a dedicatedpreamble and/or RACH resources), etc.

The WTRU may receive an activation message that may be included in theRAR message. For example, an identity or configuration of a new WTRUspecific SOM or slice which may be activated based on WTRU request.

The WTRU may receive a demodulation reference signal that may beincluded in the RAR message to decode it.

The WTRU may receive an L3 control message to provide additionalinformation (for example, a dedicated configuration, a WTRU specificcontrol channel configuration, etc.) that may be included in the RARmessage.

The WTRU may receive information on the set of TRPs that coordinated totransmit the RAR in the RAR message.

The WTRU may receive information on the TRPG in the RAR message, whichmay be associated with the TRP transmitting the RAR.

The WTRU may receive information indicating whether handover wassuccessfully performed in the RAR message. For example, an indicationmay be included to the WTRU to drop connectivity to a source TRP.

The WTRU may receive assistance information for the WTRU to beginmonitoring other TRPs/TRPGs in the RAR message.

The WTRU may receive an indication in the RAR message that previousgrants for PUSCH (for example, for SPS) are still valid.

The WTRU may receive a timing advance in the RAR message that isspecific to a TRP or a group of TRPs in a single RAR message.

The WTRU may receive an UL grant specific to one TRP or possiblydifferent UL resources for more than one TRP in the RAR message.

The WTRU may receive a temporary RNTI in the RAR message.

Referring to FIG. 10 , the WTRU may determine TRP association based onthe received at least one RAR 1006. WTRU may associate to one or moreTRPs as a function of the number of RAR messages received and theselection criteria applied by the WTRU. The selection criteria mayinclude one or more of the following: based on measurements over the RStransmitted with the RAR, based on measurements made on a previous RS(for example, the WTRU may pre-rank them beforehand), a combination ofmeasurements made with a previous RS, an RS transmitted with the RAR,ranking metric included in the payload of the RAR, earliest timing usingthe timing advance value in RAR, and timing of the RAR transmission.

The WTRU may determine association with at least one TRP based on thisrandom access procedure. The WTRU may determine a number of TRPs toassociate based on network configuration (for example, max number ofconnections may be configured in the access table), number of RARmessages that satisfy WTRU selection criteria, WTRU state (for example,the WTRU may be already connected to a serving TRP, and the WTRU mayselect the RAR received from the serving TRP), WTRU type of service/QoS(for example, ultra-reliable service may need connectivity to more thanone TRP), WTRU mobility status (for example, a stationary WTRU mayselect one TRP, WTRUs with medium/fast mobility may select more than oneTRP for seamless handover), WTRU capability (for example, the WTRU maybe restricted by number of RF chains), and the type of physical channel(for example, for a beamformed random access the WTRU may select morethan one TRP for increased robustness against link failure).

The WTRU may associate with a number of TRPs according to Min (networkconfigured max connections, number of RAR messages satisfying WTRUselection criteria, supported max connections based on WTRU capability).WTRU may indicate the selection of TRPs to the network in one of thefollowing ways: the WTRU may transmit the identities of selected TRPs ina control message (e.g., a L3 message or MSG3) in a common UL resourceconfigured for all the TRPs; the WTRU may transmit a control message onthe UL resources granted/configured by the RAR messages selected by theWTRU; and the WTRU may transmit the of selected TRPs in a controlmessage (e.g., a L3 message) to the serving cell in assistance layer(e.g., LTE-Evo eNB).

The WTRU may identify the TRPs using one or more of system signature,system signature sequence, or identity of the TRPs included in the RARmessage.

In one embodiment, TRPs may select the best RAR for the WTRU. Thecoordination between the TRPs may be distributed or centralized (forexample, in a RAN central unit). The TRPs may exchange a suitabilitymetric to determine the best TRP to serve the WTRU. The suitability mayinclude one or more of SNR on the received PRACH for a specific TRP,load on TRPs, (for example, to achieve implicit load balancing), TRPsthat already have a stored WTRU context (for example, based onhistorical association), TRPs matching WTRU capability, any otherproximity criteria, and based on WTRU's needs, for example, UL or DLheavy, or transmission type.

In another embodiment, the WTRU may determine whether to perform WTRUbased RAR selection or use network based RAR selection based on systemsignature, type of RACH resource, or based on explicit networkconfiguration in access table. In another example, the WTRU maydetermine the need to perform WTRU based RAR selection based on thenumber of RAR messages; if only one RAR message is received the WTRU mayconsider it as network based selection. If WTRU receives more than oneRAR message, then WTRU may perform RAR selection procedure as describedabove. In another example, the mode of RAR selection may be explicitlyindicated in the RAR message itself, for example with a control bit.

A hybrid solution may be also used, wherein both a network basedselection and a WTRU based selection are applied. In one example, TRPsmay coordinate to down select two or more RARs among multiple RARmessages, and the WTRU may then select one or more TRPs for association.In another example, WTRUs may receive two or more RARs and transmit theidentity of selected TRPs to the network. The network may then performthe second stage of selection and indicate the result to the WTRU in anew control message.

System signatures may be used for a rapid reconfiguration of WTRUspecific resources. The WTRU may obtain one or more pre-configurationsets, as part of dedicated signaling or cell specific signaling. Thepre-configuration set may include but is not limited to the following: ascheduling grant, another downlink or uplink control configuration,and/or a L2/L3 configuration. For example, a scheduling grant mayinclude a pre-defined resource allocation granularity (for example, one,two or more resource blocks).

Each of the preconfigured sets may be mapped to one or more systemsignature resources (for example, sequences and time/frequencyresources). The WTRU may be required to monitor the presence of systemsignatures.

The WTRU upon receiving one of the signatures may apply the associatedpre-configuration. The WTRU may be configured to transmit anacknowledgement upon activation of the pre-configured resources.Alternatively, a short control message with a few bits of informationmay be used to activate one of the pre-configured sets.

A WTRU may be configured to utilize diverse access methods, wherein eachaccess method is defined in terms of a specific combination of one ormore of UL synchronization aspect, an arrangement related to the numberof network nodes, a timing relation between a first uplink transmissionand an actual data PDU transmission, a contention resolution and/or WTRUidentification, UL resources used for access, a characteristicassociated to HARQ processing, multiple access scheme, and assistanceaspect.

For the UL synchronization aspect, the WTRU may select a differentinitial access procedure based on its UL synchronization status. Forexample, if the WTRU is required to be synchronized in the uplink beforethe data transmission, the WTRU may select a random access method toacquire UL synchronization and then perform data transfer. If the WTRUis not required to be UL synchronized, then WTRU may perform anasynchronous access method with relaxed time and frequencysynchronization requirements. In one example, two different accessmethods may be defined based on how the synchronization is performed,WTRU based or network based.

An arrangement related to the number of network nodes, for example, mayinclude a common configuration and/or UL resource across a group of TRPsthat may be reserved for multi-point initial access, wherein WTRU uplinktransmissions may be received by more than one TRP. Alternatively, theWTRU may first select a specific TRP (for example, based on suitabilitycriteria) and then may acquire initial access parameters correspondingto that TRP and subsequently perform an initial access procedure towardsthe selected TRP.

For a timing relation between first uplink transmission and actual dataPDU transmission, different initial access methods may be defined basedon a relation between the first uplink transmission and the actual dataPDU transmission. For example, the WTRU may include a portion of a dataPDU or the whole data PDU in the first uplink transmission duringinitial access. Alternatively, the WTRU may transmit one or moresignals/preambles before acquiring resources for actual data PDUtransmission.

For contention resolution and/or WTRU identification, different initialaccess methods may be defined based on whether the WTRU should confirmthat contention is resolved before data transmission, or the WTRU maytransmit data before the actual contention resolution step. For example,the WTRU may initiate a contention based data transfer and if there wasno contention, the WTRU may avoid the need for contention resolutionstep or alternatively the WTRU may be required to provide additionalidentification to resolve the contention or to identify the WTRUcontext, but this may happen after the actual data PDU transmission.

UL resources used for access includes one or more of following aspects atransmission scheme: single-carrier or multi-carrier scheme or aspecific multi-carrier scheme such as OFDM, SC-FDMA, FBMC, UFMC, zerotail or the like; a parameter associated with a transmission scheme: forexample, numerology aspects such as subcarrier spacing, symbol duration,cyclic prefix duration/guard length/zero tail length, transmit power(desired and/or compensation factor), spreading factor, bandwidth, etc.;frame structure, for example placement in time and/or frequency of oneor more reference signal(s), synchronization signals(s), physicalsignal(s)/channel(s), TTI length, frame, subframe length, TDDconfiguration etc.; scheduling aspects of the resources including amaximum number of data bits allowed, for example, depends on the size oftime frequency/code resources, MCS, repetition factor and orperiodicity, number of retries, response window etc.; and other physicalprocessing aspects, for example, spatial processing (precoding, transmitdiversity, spatial multiplexing), beamforming (analog, digital orhybrid), etc.

For a characteristic associated with HARQ processing, different initialaccess methods may be defined based on whether HARQ is used for the datatransfer and HARQ parameters such as a number of HARQ processes,relative timing between scheduling grants, transmission/reception ofdata and transmission/reception of HARQ feedback, etc.

For multiple access schemes, different initial access schemes may bedefined based on the type of multiple access used, for example, resourcespread multiple access, sparse code multiple access, contention basedaccess, scheduled access, etc. Each initial access scheme may beassociated with parameters specific to a multiple access scheme (forexample, a random access power level, preamble, power ramping factor,max number of retransmissions etc., time frequency resource pattern,spreading code, sparse code etc.). In one embodiment, resources may begrouped according to the multiple access scheme, for example, groups ofWTRUs may be pre-configured (for example, via dedicated RRC signaling)for a common grant less resource that may be accessed by WTRUsautonomously, groups of resources may be configured (for example, via anaccess table) for contention based access that may be accessed by allWTRUs in the cell, groups of resources may be configured (for example,via downlink control information) for scheduled access that may beaccessed only by WTRUs that have a valid WTRU specific scheduling grant.

For the assistance aspect, the WTRU may perform initial access on anassisted carrier/cell/cell group/slice/SOM based on assistanceinformation received from assistance carrier/cell/cell group/slice/SOM.Such assistance information includes one or more characteristics of theaccess method described above.

Various access methods may be performed by the WTRU.

One example access method includes the WTRU transmitting data on acontention based data channel. The first uplink message from the WTRU(for example, msg1) may carry a whole data PDU or portions of it. TheWTRU may also transmit a demodulation reference signals, preambles,and/or the WTRU identity along with msg1. The WTRU may choose thedemodulation reference signal from a pool of available sequences.Alternatively, the WTRU may choose the demodulation reference signal asa function of the WTRU identity. In another embodiment, the WTRU may beconfigured with a unique demodulation reference signal and/or anexplicit WTRU identity. The WTRU may receive an acknowledgement from thenetwork which includes one or more of the following: a reference to theUL data PDU (for example, time/frequency resource occupied by the dataPDU), demodulation reference signal sequence used in the UL PDU, WTRU IDincluded in the data PDU, etc.

A second example access method is based on multi-point random access asdescribed above. Other example access methods may include but are notlimited to: beamformed random access for above 6 GHz, access methodsspecific to coverage enhanced WTRUs using repetition, asynchronousaccess method with relaxed synchronization requirements.

Configuration of diverse access methods may include one or morecharacteristics/properties/parameters listed above, including theresources to be used for the access method.

FIG. 11 is a flow diagram of an example procedure 1100 for configurationof diverse access methods that may be performed in the example system700 described above and used in combination with any of the embodimentsdescribed herein. While each step of the procedure 1100 in FIG. 11 isshown and described separately, multiple steps may be executed in adifferent order than what is shown, in parallel with each other, orconcurrently with each other. The process of FIG. 11 is performed by aWTRU for exemplary purposes, but it may also be performed by any nodeoperating in a wireless communications system such as a TRP, eNB, 5gNB,AP, or base station. In the example of FIG. 11 , a WTRU, via thetransceiver or receiver of the WTRU as described above, may receive aconfiguration for at least one diverse access method 1101. Thisreception of a at least one diverse access method 1101 may be achievedaccording to at least one of the following: via a default access method,a broadcasted configuration, a particular arrangement of systemsignatures, an access table, a dedicated configuration, an assistedconfiguration, and/or an implicit determination.

For example, a default access method may be pre-configured and the WTRUmay use the default access method in the absence of any otherconfiguration or until it has acquired any of the configurationsdescribed below.

A broadcasted configuration may include a list of allowed/possibleaccess methods may be broadcasted e.g., using RRC msg (including systeminformation messages), MAC control element (in a shared schedulinginformation on a common channel and/or initial access response message(for example, a RAR received during random access procedure)), masterinformation block (which may include for example the initial accessmethod used on a generic SOM/slice or when detailed access table is notyet acquired/available), system information broadcast (which may includeaccess methods allowed in a specific SOM/slice which may or may notcarry system information broadcast).

For using a particular arrangement of system signatures, a predefinedsignal sequence may be used and/or relative timing/frequency offsetbetween such signals may be used (for example, an access method may beindicated and/or determined as a function of index associated with thesequence of broadcast signal and/or relative placement (intime/frequency) between the plurality of such signals).

A configuration for one or more access methods may be provided in theaccess table, which may be indexed by a system signature or a reservedvalue. For example, each access method may be associated with adifferent system signature, and such an association may additionallyimply a mapping between a bandwidth region where the system signature istransmitted and the applicable access method within the associatedbandwidth region. The WTRU may obtain the access table transmitted usinga broadcast mechanism (for example, via a shared data channel) or usinga dedicated channel (for example, as a WTRU specific RRC configuration).

For a dedicated configuration, the WTRU may be explicitly configuredwith one or more access methods/parameters using a control protocol (forexample, RRC protocol), medium access protocol (for example, MAC controlelement or by means of RAR message during a random access procedure), apaging message may be used to indicate both a DL data arrival and theassociated UL access method/parameters to use, a NAS message (forexample, a WTRU may receive set of allowed access methods duringattachment, and it may be a function of WTRU subscription), downlinkcontrol signaling (for example, by means of a DCI received, additionallythe DCI may indicate the resources or slices where the access methodsare applicable). The WTRU may prioritize the dedicated configurationover other configurations. For example, one or more parameters in thededicated configuration may take precedence over parameters configuredthrough other means.

For an assisted configuration, the WTRU may obtain the configuration foran access method from an assistance layer. Such a configuration may beprovided via a RRC configuration or may be signaled using access table.For example an access method configuration for the small cell layer maybe provided by a macro layer. In another example, the configuration fora beamformed small cell layer (operating for example above 6 GHz) may beprovided by the assistance layer operating in the sub 6 GHz frequency.

For an implicit determination, the WTRU may implicitly identify one ormore aspects of access method from the configuration of rest of theparameters. For example, the choice of multiple access method may beimplicitly determined by the nature of resource allocation and/orparameterization of the UL resources.

Configuration aspects may include the information necessary for the WTRUto identify different access methods, select an appropriate accessmethod (for example, information applicable to access method selection)and to perform access procedure. One or more configuration aspects ofthe access method may be static, whereas the others may be dynamic. Inone example, the WTRU may combine parts of configurations signaled usingdifferent methods to obtain an overall configuration for an accessmethod. For example, a choice of multiple access method may be signaledin a broadcast system information/access table, and the resources forthe access method may be dynamically scheduled via a control channel.Additionally, the WTRU may obtain parts of the configuration fromdifferent nodes to determine the overall configuration for an accessmethod. The WTRU may obtain assistance from a macro layer, combined withspecific information from small cell layers to perform initial access onthe small cell layer. The WTRU may receive a configuration of ULresources independent of the access methods. For example, a linkage maybe provided between the UL resources and the access method to be used onthat UL resource. In another example, a specific slice isolated fromother slices may be reserved for initial access procedures.

Referring to FIG. 11 , the WTRU may trigger at least one initial accessprocedure 1102. This step may be performed when one or more of thefollowing conditions are satisfied:

There is an arrival of UL data and/or higher layer signaling (forexample, RRC, NAS) and one or more of the following conditions aresatisfied: when WTRU UL synchronization status is non-synchronized; databelongs to a logical channel or logical channel group for which noconnection exists, irrespective of the status of other logical channels(for example, being active or inactive); data belongs to a new logicalchannel group or logical channel for which no transport channel mappingexists; data is for a different service than the services that arecurrently active; data belongs to the logical channel which isassociated with a different mode/slice/SOM than the currently activelogical channel; data on the LCH is configured to be transmitted to aTRP for which WTRU doesn't have UL synchronization; data is for which nodefined configuration/i.e. radio bearers or logical channels exist; anddata is mapped to a different layer or RAT or component carrier or cellgroup than the currently active layer/RAT/component carrier or cellgroup.

There is DL data arrival and one or more of the following conditions aresatisfied: the WTRU receives a paging message or a signal indicating DLdata arrival and the paging message may additionally indicate a newlogical channel/transport channel configuration; there is an explicitindication in a paging message to trigger a specific access method,which may be on a specific SOM and/or slice; and for example, the DLpaging message may indicate DL data arrival, along with either a logicalchannel identity and/or mapping to a specific transport channel typeand/or explicit indication of initial access method.

There are aspects related to new or unknown system signatures: the WTRUmay be preconfigured to detect new signatures and trigger a report tothe network. Reception of an unknown system signature for which no validentry in the access table exists may occur, for example, when a TRPtransitions from an OFF state to ON state, or when a new slice or SOM isinstantiated and a system signature specific to that slice/SOM istransmitted. Alternatively, the WTRU may view unknown signatures simplyas a non-accessible transmission point or slice or SOM.

The L3 is re-established (for example, RRC connection): for example, theL3 may be re-established due to a failure such as a radio link failure,handover failure, or security failure. The WTRU may be configured toinitiate an access procedure for the purposes of reporting the invalidconfiguration and/or to resume the data transfer. For example, when theWTRU may be unable to comply with one or more aspects of a configurationreceived in access table or higher layer message (for example, L3) orMAC Control element or any other means.

An initial access procedure is triggered by mobility of the WTRU: forexample, an initial access procedure may be triggered when the WTRUmoves into a new RAN routing area that is different from the previousarea or not included in the previous RAN routing area group, or a changeof RAN routing area, TRPG or RAN central unit and handover.

There are aspects related to UL synchronization and timing advance: theWTRU may lose UL synchronization (for example, the WTRU may be requiredto maintain UL synchronization for low latency transfer); forpositioning purposes, when timing advance is needed for WTRUpositioning; and time elapsed, periodic such as when WTRU enters DRX butstill needs to maintain UL synchronization.

In the case of LTE-assisted 5gFLEX transport channels: the WTRU monitorspreconfigured time/frequency resources within LTE Uu for 5GFlexoperation. The WTRU may trigger initial access when it detects one ormore system signatures and/or when the received power of the systemsignatures is above a threshold in the resources configured for 5GFlexoperation.

The WTRU receives an explicit order from the network (for example, whenthe network orders the WTRU to transition from asynchronous access tosynchronous access, PDCCH order, and/or network triggered initial access(for example to retrieve unknown WTRU context)).

The WTRU changes coverage status: including moving back to in-coveragefrom out-of-coverage, when the serving cell quality drops below athreshold, and when WTRU enters enhanced coverage mode. The WTRU mayinitiate initial access corresponding to enhanced coverage mode (forexample, repetition of RACH preambles).

The WTRU is unable to acquire access table within time elapsed: forexample, the WTRU may use a default access method on a low periodicresource that may be a function of system signature.

The WTRU triggers at least one access procedure upon power up.

The WTRU triggers at least one access procedure upon activation of ULresources corresponding to a different access method: including when anew slice or SOM is activated and one or more UL resources in theslice/SOM is reserved for initial access. The WTRU may perform theinitial access method associated and/or configured for that SOM orslice. When a new component carrier (for example, in case of carrieraggregation) or when a small cell is added (for example, in case ofmulti-connectivity), the WTRU may trigger the initial access methodconfigured for that carrier or small cell, etc. For example, when above6 GHz carrier is activated, the WTRU may then perform initial access(for example, beamformed initial access) specific to that carrier.

There is a trigger to a new/secondary access method as an outcome of theprimary access method or failure of the previous access method. Triggersmay be specific to D2D or relay mode.

Referring to FIG. 11 , the WTRU may select at least one access method ofa plurality of access methods 1103. This selection may be according tovarious selection criteria. WTRU may determine the UL resourcesassociated with and configured for the selected access method. WTRU maythen perform the at least one access procedure 1104. This may beperformed according to the rules defined for the access method.

The selection criteria used to select the at least one access method mayinclude but is not limited to the following: as a function of a logicalchannel type for which data becomes available; based on the outcome of aprevious initial access procedure; based on the outcome of a primaryinitial access procedure; as a function of a size of the data PDU; as afunction of a type of the data PDU (for example, IP or non-IP data); asa function of the service request type; as a function of the existingLCH connections/link; a type of connection; as a function of an accessclass; as a function of the radio interface; as a function of signalstructure, SOM, or bandwidth region; as a function of slice; as afunction of Type of Service/QoS; as a function of TRP cell groupspecific, TRP specific, TRPG specific; as a function of a layer; aconfiguration aspect; based on resource selection; generic accessmethods and specific access methods; as a function of a received systemsignature; as a function of the capability and/or subscription of theWTRU; based on the coverage status of the WTRU; based on a function ofthe operation mode; based on more than one initial access procedure inparallel.

For a function of logical channel type for which data becomes available,different types of radio bearer and/or logical channels and/or logicalconnections, logical channel groups and/or transport channels and amapping between them may be defined to characterize different types ofend to end service (for example, eMBB, URLLC, or mMTC) to be supportedby the 5GFlex. Each logical channel and/or transport channel may beassociated with one or more access methods. Upon arrival of data for anempty logical channel, the WTRU may first select one (if more than oneexist) and then perform the initial access procedure associated withthat LCH.

When based on the outcome of a previous initial access procedure, theWTRU may maintain a count of number of failures with a particular accessmethod. The WTRU may switch to a different access method when the numberof failures exceeds a predefined threshold. Additionally, the failedaccess method may be barred for a predefined time specified, forexample, via a prohibit timer. The WTRU may retry a failed access methodwith different parameters (including but not limited to power ramp,increased repetition, and different resources reserved/prioritized forcolliding WTRUs (for example, some dedicated resources)). The WTRU maydeclare a radio link failure when all or a set of initial access methodsor a counter across all access methods exceeds a threshold or when apredefined time elapses from the start of the initial access procedure.

The selection may be based on the outcome of a primary initial accessprocedure, for example, when the primary initial access procedureprovides more information about the secondary initial access procedure.There may be a redirection to another in case of SOM.

The selection may be a function of existing LCH connections/links. Forexample, upon arrival of data in a new LCH the WTRU may use specificmethods corresponding to the current active LCH, TCH, slice, SOM (forexample, using current UL control channel).

The selection may be based on type of connection. The WTRU may beconfigured to perform a connection based data transfer or aconnectionless data transfer, for example, based on a size of the dataPDU, latency, and/or overhead requirements. The WTRU may selectdifferent access methods associated with the nature of the connection.For example, the connection may be based on a random access procedurefor a connection oriented data transfer, a contention based datatransfer procedure for connectionless data transfer, an establishmentcause (MO signaling or MO data), re-establishment or establishment, highpriority access, delay tolerant access, emergency connection, etc.

The selection may be a function of an access class. The WTRU may selectdifferent access methods based on an access class, and some of theaccess methods may be restricted for certain access classes.

The WTRU may select the access method as a function of the radiointerface. For example, different access methods may be defined for LTE,LTEEvo, 5GFlex below 6 GHz, and 5GFlex above 6 GHz. The WTRU may selectone access method out of possible access methods for each of the radiointerfaces. The WTRU may prioritize selection of radio interfaces basedon an allowed access method that meets one or more requirements in termsof latency and/or overhead.

The selection may be a function of the signal structure, SOM, orbandwidth region. There may be a set of allowed resources within theSOM. The WTRU may select a SOM and then perform access method associatedwith it.

The selection may be a function of slice (type of slice). The WTRU mayperform an initial access method on a particular slice according to thetype of service provided by the slice (function of system signature).

The selection may be a function of a layer. The access method may alsobe determined from a property associated with the node, such as anindication of a layer.

The selection may be based on a configuration aspect. For example, theWTRU may be configured with a specific access method for the DL dataarrival in the DL paging message. The WTRU may trigger the configuredaccess method to use in the target cell upon handover.

The selection may be based on resource selection. The WTRU may determinethe access method based on, for example, the UL resource selection. TheWTRU may select an earliest occurring UL resource and then select theaccess method associated/configured for that resource. Among theavailable access methods, WTRU may choose one as a function of itsreducing latency aspect. The WTRU may compare the scheduling periodicityof different access methods/resources and select the earliest or onewith least overhead, etc.

The selection may be based on a generic access method and/or a specificaccess method. The WTRU may first select a default access methodconfigured for/associated with a generic SOM/slice/preferred cells/RATsand subsequently perform specific access methods associated with otherSOMs/slices/cells/cell groups/RATs. The specific access methods may beconfigured/activated as a result of default access method. In onesolution the default access method may be cell specific, and thespecific access method may be WTRU specific. For example, there may be adistinction between the initial access using the nominal bandwidth (forexample, power on, obtaining PDP context, etc.) and an initial accessfor a specific SOM, which may be associated with a given signature. SomeeNBs/TRPs may support only one, the other, or both. For example, a macroeNB may support access using a nominal SOM, while TRPs may support onlySOM-specific access (no means to exchange L3/NAS signaling), whileothers (eNBs or TRPs) may support both.

The selection may be a function of a received system signature. The WTRUmay select the initial access method associated with/configured for thereceived system signature. For example, when the WTRU receives multiplesystem signatures, the WTRU may select the initial access methodassociated with the system signatures of a highest received power orpreferred type of system signature.

The selection may be based on coverage status of the WTRU, which mayinclude in-coverage, out of coverage, enhanced coverage, etc. Functionof operation mode may include different access methods based on whetherthe operating mode is infrastructure mode, D2D mode, relay mode ortransport (for example, self-backhaul/fronthaul) mode. More than oneinitial access procedure may be used in parallel.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, AP, eNB, 5gNB, terminal, base station, RNC, or any hostcomputer.

What is claimed is:
 1. A wireless transmit/receive unit (WTRU)comprising: a processor; and a transceiver; the transceiver configuredto receive a transmission including information associated with aplurality of random access channel (RACH) configurations, theinformation indicating a plurality of RACH occasions in which a preambletransmission may be sent; the transceiver configured to receive one ormore reference signals; the transceiver and the processor configured tosend, using one of the plurality of RACH configurations, the preambletransmission in one of the plurality of RACH occasions along with one ormore protocol data units (PDUs), wherein the one of the plurality ofRACH configurations is selected based on a measurement of at least oneof the one or more received reference signals; and the transceiver andthe processor configured to receive a random access response, whereinthe random access response is responsive to the preamble transmissionand the one or more PDUs.
 2. The WTRU of claim 1, wherein thetransmission including the information associated with the plurality ofRACH configurations includes a plurality of power ramping parameters,each one of the plurality of power ramping parameters associated withone of the plurality of RACH configurations.
 3. The WTRU of claim 2,wherein the preamble transmission is sent using a power settingdetermined based on the selected RACH configuration and based on acorresponding one of the plurality of power ramping parameters.
 4. TheWTRU of claim 1, wherein at least two of the RACH configurations areassociated with different spectrum operating modes, and wherein, inaccordance with each of the different spectrum operating modes, thetransceiver is configured to send uplink transmissions in a differentuplink bandwidth.
 5. The WTRU of claim 1, wherein the preambletransmission is sent prior to the sending of the one or more PDUs. 6.The WTRU of claim 1, wherein each of the plurality of RACHconfigurations is associated with a time window for receiving a randomaccess response, and wherein the random access response is receivedwithin a time window associated with the selected RACH configuration. 7.The WTRU of claim 1, wherein the random access response includesinformation indicating that contention between the WTRU and another WTRUis resolved.
 8. The WTRU of claim 1, wherein the information associatedwith the plurality of random access channel (RACH) configurationsincludes criteria for selecting a preamble to be included in thepreamble transmission.
 9. The WTRU of claim 8, wherein the criteria forselecting the preamble to be included in the preamble transmission isbased on a measurement of the received one or more reference signalsthat corresponds to a beam of a transmit/receive point (TRP).
 10. Amethod performed by a wireless transmit/receive unit (WTRU), the methodcomprising: receiving a transmission including information associatedwith a plurality of random access channel (RACH) configurations, theinformation indicating a plurality of RACH occasions in which a preambletransmission may be sent; receiving one or more reference signals;sending, using a first one of the plurality of RACH configurations, thepreamble transmission in one of the plurality of RACH occasions alongwith one or more protocol data units (PDUs), wherein the one of theplurality of RACH configurations is selected based on a measurement ofat least one of the one or more received reference signals; andreceiving a random access response, wherein the random access responseis responsive to the preamble transmission and the one or more PDUs. 11.The method of claim 10, wherein the transmission including theinformation associated with the plurality of RACH configurationsincludes a plurality of power ramping parameters, each one of theplurality of power ramping parameters associated with one of theplurality of RACH configurations.
 12. The method of claim 11, whereinthe preamble transmission is sent using a power setting determined basedon the selected RACH configuration and based on a corresponding one ofthe plurality of power ramping parameters.
 13. The method of claim 10,wherein at least two of the RACH configurations are associated withdifferent spectrum operating modes, and wherein, in accordance with eachof the different spectrum operating modes, the transceiver is configuredto send uplink transmissions in a different uplink bandwidth.
 14. Themethod of claim 10, wherein the preamble transmission is sent prior tothe sending of the one or more PDUs.
 15. The method of claim 10, whereineach of the plurality of RACH configurations is associated with a timewindow for receiving a random access response, and wherein the randomaccess response is received within a time window associated with theselected RACH configuration.
 16. The method of claim 10, wherein therandom access response includes information indicating that contentionis resolved.
 17. The method of claim 10, wherein the informationassociated with the plurality of random access channel (RACH)configurations includes criteria for selecting a preamble to be includedin the preamble transmission.
 18. The method of claim 17, wherein thecriteria for selecting the preamble to be included in the preambletransmission is based on a measurement of the received one or morereference signals that corresponds to a beam of a transmit/receive point(TRP).